fix possible integer overflow in alloc()#109
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If n is close to 2**32 then the alignment calculation could cause an integer overflow. Rule this out by checking if the allocation is smaller than the fixed buffer. It could be done by checking against the possible space, which is done later anyway, but checking against SPACE has the benefit that this is a constant.
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* it's as simple as possible, probably intentional. This makes things like alloc_re() (i.e. realloc()) inefficient as it does not look if the thing it reallocates is already the last thing in the batch, and simply extends that, or if alloc_free() has the last block and adds things back to the pool (ideally with zeroing for security reasons). * it makes it basically impossible to detect overruns on early small allocations with tools like valgrind, address sanitizer or friends as those allocations never hit malloc(), so are never traced by any custom tools. Any overrun will just go into the next variable, untracable. * allocators do their own buffering, alignment, and so on. If they are broken, your system is severely screwed. And if we need more money^H^H^H^Hemory we will hit that buggy allocatator anyway, making things harder to detect as it will only happen on "heavy" memory usage. This is not TruOS, SunOS 1.x or something like that anymore. We expect a reasonably sane OS. Everything else will get us screwed in much more severe ways. * it has shown issues when coming close to 4GiB allocations (#37, #109, older reports). DJB correctly says that an allocation of that size in your mailer shows that you have already done something wrong, but still: 64 bit platforms are the default, so using a 32 bit type to pass allocation sizes is a bug of it's own. * why bother at all with having a custom allocator?
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* it's as simple as possible, probably intentional. This makes things like alloc_re() (i.e. realloc()) inefficient as it does not look if the thing it reallocates is already the last thing in the batch, and simply extends that, or if alloc_free() has the last block and adds things back to the pool (ideally with zeroing for security reasons). * it makes it basically impossible to detect overruns on early small allocations with tools like valgrind, address sanitizer or friends as those allocations never hit malloc(), so are never traced by any custom tools. Any overrun will just go into the next variable, untracable. * allocators do their own buffering, alignment, and so on. If they are broken, your system is severely screwed. And if we need more money^H^H^H^Hemory we will hit that buggy allocatator anyway, making things harder to detect as it will only happen on "heavy" memory usage. This is not TruOS, SunOS 1.x or something like that anymore. We expect a reasonably sane OS. Everything else will get us screwed in much more severe ways. * it has shown issues when coming close to 4GiB allocations (#37, #109, older reports). DJB correctly says that an allocation of that size in your mailer shows that you have already done something wrong, but still: 64 bit platforms are the default, so using a 32 bit type to pass allocation sizes is a bug of it's own. * why bother at all with having a custom allocator?
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* it's as simple as possible, probably intentional. This makes things like alloc_re() (i.e. realloc()) inefficient as it does not look if the thing it reallocates is already the last thing in the batch, and simply extends that, or if alloc_free() has the last block and adds things back to the pool (ideally with zeroing for security reasons). * it makes it basically impossible to detect overruns on early small allocations with tools like valgrind, address sanitizer or friends as those allocations never hit malloc(), so are never traced by any custom tools. Any overrun will just go into the next variable, untracable. * allocators do their own buffering, alignment, and so on. If they are broken, your system is severely screwed. And if we need more money^H^H^H^Hemory we will hit that buggy allocatator anyway, making things harder to detect as it will only happen on "heavy" memory usage. This is not TruOS, SunOS 1.x or something like that anymore. We expect a reasonably sane OS. Everything else will get us screwed in much more severe ways. * it has shown issues when coming close to 4GiB allocations (#37, #109, older reports). DJB correctly says that an allocation of that size in your mailer shows that you have already done something wrong, but still: 64 bit platforms are the default, so using a 32 bit type to pass allocation sizes is a bug of it's own. * why bother at all with having a custom allocator?
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* it's as simple as possible, probably intentional. This makes things like alloc_re() (i.e. realloc()) inefficient as it does not look if the thing it reallocates is already the last thing in the batch, and simply extends that, or if alloc_free() has the last block and adds things back to the pool (ideally with zeroing for security reasons). * it makes it basically impossible to detect overruns on early small allocations with tools like valgrind, address sanitizer or friends as those allocations never hit malloc(), so are never traced by any custom tools. Any overrun will just go into the next variable, untracable. * allocators do their own buffering, alignment, and so on. If they are broken, your system is severely screwed. And if we need more money^H^H^H^Hemory we will hit that buggy allocatator anyway, making things harder to detect as it will only happen on "heavy" memory usage. This is not TruOS, SunOS 1.x or something like that anymore. We expect a reasonably sane OS. Everything else will get us screwed in much more severe ways. * it has shown issues when coming close to 4GiB allocations (#37, #109, older reports). DJB correctly says that an allocation of that size in your mailer shows that you have already done something wrong, but still: 64 bit platforms are the default, so using a 32 bit type to pass allocation sizes is a bug of it's own. * why bother at all with having a custom allocator?
DerDakon
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* it's as simple as possible, probably intentional. This makes things like alloc_re() (i.e. realloc()) inefficient as it does not look if the thing it reallocates is already the last thing in the batch, and simply extends that, or if alloc_free() has the last block and adds things back to the pool (ideally with zeroing for security reasons). * it makes it basically impossible to detect overruns on early small allocations with tools like valgrind, address sanitizer or friends as those allocations never hit malloc(), so are never traced by any custom tools. Any overrun will just go into the next variable, untracable. * allocators do their own buffering, alignment, and so on. If they are broken, your system is severely screwed. And if we need more money^H^H^H^Hemory we will hit that buggy allocator anyway, making things harder to detect as it will only happen on "heavy" memory usage. This is not TruOS, SunOS 1.x or something like that anymore. We expect a reasonably sane OS. Everything else will get us screwed in much more severe ways. * it has shown issues when coming close to 4GiB allocations (#37, #109, older reports). DJB correctly says that an allocation of that size in your mailer shows that you have already done something wrong, but still: 64 bit platforms are the default, so using a 32 bit type to pass allocation sizes is a bug of it's own. * why bother at all with having a custom allocator?
DerDakon
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* it's as simple as possible, probably intentional. This makes things like alloc_re() (i.e. realloc()) inefficient as it does not look if the thing it reallocates is already the last thing in the batch, and simply extends that, or if alloc_free() has the last block and adds things back to the pool (ideally with zeroing for security reasons). * it makes it basically impossible to detect overruns on early small allocations with tools like valgrind, address sanitizer or friends as those allocations never hit malloc(), so are never traced by any custom tools. Any overrun will just go into the next variable, untracable. * allocators do their own buffering, alignment, and so on. If they are broken, your system is severely screwed. And if we need more money^H^H^H^Hemory we will hit that buggy allocator anyway, making things harder to detect as it will only happen on "heavy" memory usage. This is not TruOS, SunOS 1.x or something like that anymore. We expect a reasonably sane OS. Everything else will get us screwed in much more severe ways. * it has shown issues when coming close to 4GiB allocations (#37, #109, older reports). DJB correctly says that an allocation of that size in your mailer shows that you have already done something wrong, but still: 64 bit platforms are the default, so using a 32 bit type to pass allocation sizes is a bug of it's own. * when any additional patch accidentially mixes calls to this functions with normal realloc()/free() this can lead to random crashes * why bother at all with having a custom allocator?
DerDakon
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May 12, 2020
* it's as simple as possible, probably intentional. This makes things like alloc_re() (i.e. realloc()) inefficient as it does not look if the thing it reallocates is already the last thing in the batch, and simply extends that, or if alloc_free() has the last block and adds things back to the pool (ideally with zeroing for security reasons). * it makes it basically impossible to detect overruns on early small allocations with tools like valgrind, address sanitizer or friends as those allocations never hit malloc(), so are never traced by any custom tools. Any overrun will just go into the next variable, untracable. * allocators do their own buffering, alignment, and so on. If they are broken, your system is severely screwed. And if we need more money^H^H^H^Hemory we will hit that buggy allocator anyway, making things harder to detect as it will only happen on "heavy" memory usage. This is not TruOS, SunOS 1.x or something like that anymore. We expect a reasonably sane OS. Everything else will get us screwed in much more severe ways. * it has shown issues when coming close to 4GiB allocations (#37, #109, older reports). DJB correctly says that an allocation of that size in your mailer shows that you have already done something wrong, but still: 64 bit platforms are the default, so using a 32 bit type to pass allocation sizes is a bug of it's own. * when any additional patch accidentially mixes calls to this functions with normal realloc()/free() this can lead to random crashes * why bother at all with having a custom allocator?
DerDakon
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May 12, 2020
* it's as simple as possible, probably intentional. This makes things like alloc_re() (i.e. realloc()) inefficient as it does not look if the thing it reallocates is already the last thing in the batch, and simply extends that, or if alloc_free() has the last block and adds things back to the pool (ideally with zeroing for security reasons). * it makes it basically impossible to detect overruns on early small allocations with tools like valgrind, address sanitizer or friends as those allocations never hit malloc(), so are never traced by any custom tools. Any overrun will just go into the next variable, untracable. * allocators do their own buffering, alignment, and so on. If they are broken, your system is severely screwed. And if we need more money^H^H^H^Hemory we will hit that buggy allocator anyway, making things harder to detect as it will only happen on "heavy" memory usage. This is not TruOS, SunOS 1.x or something like that anymore. We expect a reasonably sane OS. Everything else will get us screwed in much more severe ways. * it has shown issues when coming close to 4GiB allocations (#37, #109, older reports). DJB correctly says that an allocation of that size in your mailer shows that you have already done something wrong, but still: 64 bit platforms are the default, so using a 32 bit type to pass allocation sizes is a bug of it's own. * when any additional patch accidentially mixes calls to this functions with normal realloc()/free() this can lead to random crashes * why bother at all with having a custom allocator?
DerDakon
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* it's as simple as possible, probably intentional. This makes things like alloc_re() (i.e. realloc()) inefficient as it does not look if the thing it reallocates is already the last thing in the batch, and simply extends that, or if alloc_free() has the last block and adds things back to the pool (ideally with zeroing for security reasons). * it makes it basically impossible to detect overruns on early small allocations with tools like valgrind, address sanitizer or friends as those allocations never hit malloc(), so are never traced by any custom tools. Any overrun will just go into the next variable, untracable. * allocators do their own buffering, alignment, and so on. If they are broken, your system is severely screwed. And if we need more money^H^H^H^Hemory we will hit that buggy allocator anyway, making things harder to detect as it will only happen on "heavy" memory usage. This is not TruOS, SunOS 1.x or something like that anymore. We expect a reasonably sane OS. Everything else will get us screwed in much more severe ways. * it has shown issues when coming close to 4GiB allocations (#37, #109, older reports). DJB correctly says that an allocation of that size in your mailer shows that you have already done something wrong, but still: 64 bit platforms are the default, so using a 32 bit type to pass allocation sizes is a bug of it's own. * when any additional patch accidentially mixes calls to this functions with normal realloc()/free() this can lead to random crashes * why bother at all with having a custom allocator?
DerDakon
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May 22, 2020
* it's as simple as possible, probably intentional. This makes things like alloc_re() (i.e. realloc()) inefficient as it does not look if the thing it reallocates is already the last thing in the batch, and simply extends that, or if alloc_free() has the last block and adds things back to the pool (ideally with zeroing for security reasons). * it makes it basically impossible to detect overruns on early small allocations with tools like valgrind, address sanitizer or friends as those allocations never hit malloc(), so are never traced by any custom tools. Any overrun will just go into the next variable, untracable. * allocators do their own buffering, alignment, and so on. If they are broken, your system is severely screwed. And if we need more money^H^H^H^Hemory we will hit that buggy allocator anyway, making things harder to detect as it will only happen on "heavy" memory usage. This is not TruOS, SunOS 1.x or something like that anymore. We expect a reasonably sane OS. Everything else will get us screwed in much more severe ways. * it has shown issues when coming close to 4GiB allocations (#37, #109, older reports). DJB correctly says that an allocation of that size in your mailer shows that you have already done something wrong, but still: 64 bit platforms are the default, so using a 32 bit type to pass allocation sizes is a bug of it's own. * when any additional patch accidentially mixes calls to this functions with normal realloc()/free() this can lead to random crashes * why bother at all with having a custom allocator?
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If n is close to 2**32 then the alignment calculation could cause an integer overflow. Rule this out by checking if the allocation is smaller than the fixed buffer. It could be done by checking against the possible space, which is done later anyway, but checking against SPACE has the benefit that this is a constant.
Alternative implementation for #37.