Fix readdir() bug when a non-zero offset is specified in filler #269
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Thanks for tracking this down! I think your fix is fine. I have just one request: could you please also add a comment to ChangeLog.rst? |
added 2 commits
July 20, 2018 20:25
Test that after reading the whole directory with readdir(), the offsets returned by telldir() are still valid.
The bug occurs when a filesystem client reads a directory until the end,
seeks using seekdir() to some valid non-zero position and calls
readdir(). A valid 'struct dirent *' is expected, but NULL is returned
instead. Pseudocode demonstrating the bug:
DIR *dp = opendir("some_dir");
struct dirent *de = readdir(dp);
/* Get offset of the second entry */
long offset = telldir(dp);
/* Read directory until the end */
while (de)
de = readdir(de);
seekdir(dp, offset);
de = readdir(dp);
/* de must contain the second entry, but NULL is returned instead */
The reason of the bug is that when the end of directory is reached, the
kernel calls FUSE_READDIR op with an offset at the end of directory, so
the filesystem's .readdir callback never calls the filler function, and
we end up with dh->filled set to 1. After seekdir(), FUSE_READDIR is
called again with a new offset, but this time the filesystem's .readdir
callback is never called, and an empty reply is returned.
Fix by setting dh->filled to 1 only when zero offsets are given to
filler function.
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Thanks for review! I've added comments to |
rostislav
added a commit
to rostislav/libfuse
that referenced
this pull request
Jul 24, 2018
The bug occurs when a filesystem client reads a directory until the end,
seeks using seekdir() to some valid non-zero position and calls
readdir(). A valid 'struct dirent *' is expected, but NULL is returned
instead. Pseudocode demonstrating the bug:
DIR *dp = opendir("some_dir");
struct dirent *de = readdir(dp);
/* Get offset of the second entry */
long offset = telldir(dp);
/* Read directory until the end */
while (de)
de = readdir(de);
seekdir(dp, offset);
de = readdir(dp);
/* de must contain the second entry, but NULL is returned instead */
The reason of the bug is that when the end of directory is reached, the
kernel calls FUSE_READDIR op with an offset at the end of directory, so
the filesystem's .readdir callback never calls the filler function, and
we end up with dh->filled set to 1. After seekdir(), FUSE_READDIR is
called again with a new offset, but this time the filesystem's .readdir
callback is never called, and an empty reply is returned.
Fix by setting dh->filled to 1 only when zero offsets are given to
filler function.
This commit is backported from the following commit in 'master' branch:
commit 5f125c5 (myfork/master)
Author: Rostislav <rostislav@users.noreply.github.com>
Date: Sat Jul 21 12:57:09 2018 +0300
Fix readdir() bug when a non-zero offset is specified in filler (libfuse#269)
rostislav
pushed a commit
to rostislav/libfuse
that referenced
this pull request
Jul 25, 2018
The bug occurs when a filesystem client reads a directory until the end,
seeks using seekdir() to some valid non-zero position and calls
readdir(). A valid 'struct dirent *' is expected, but NULL is returned
instead. Pseudocode demonstrating the bug:
DIR *dp = opendir("some_dir");
struct dirent *de = readdir(dp);
/* Get offset of the second entry */
long offset = telldir(dp);
/* Read directory until the end */
while (de)
de = readdir(de);
seekdir(dp, offset);
de = readdir(dp);
/* de must contain the second entry, but NULL is returned instead */
The reason of the bug is that when the end of directory is reached, the
kernel calls FUSE_READDIR op with an offset at the end of directory, so
the filesystem's .readdir callback never calls the filler function, and
we end up with dh->filled set to 1. After seekdir(), FUSE_READDIR is
called again with a new offset, but this time the filesystem's .readdir
callback is never called, and an empty reply is returned.
Fix by setting dh->filled to 1 only when zero offsets are given to
filler function.
This commit is backported from the following commit in 'master' branch:
commit 5f125c5
Author: Rostislav <rostislav@users.noreply.github.com>
Date: Sat Jul 21 12:57:09 2018 +0300
Fix readdir() bug when a non-zero offset is specified in filler (libfuse#269)
rostislav
pushed a commit
to rostislav/libfuse
that referenced
this pull request
Jul 25, 2018
The bug occurs when a filesystem client reads a directory until the end,
seeks using seekdir() to some valid non-zero position and calls
readdir(). A valid 'struct dirent *' is expected, but NULL is returned
instead. Pseudocode demonstrating the bug:
DIR *dp = opendir("some_dir");
struct dirent *de = readdir(dp);
/* Get offset of the second entry */
long offset = telldir(dp);
/* Read directory until the end */
while (de)
de = readdir(de);
seekdir(dp, offset);
de = readdir(dp);
/* de must contain the second entry, but NULL is returned instead */
The reason of the bug is that when the end of directory is reached, the
kernel calls FUSE_READDIR op with an offset at the end of directory, so
the filesystem's .readdir callback never calls the filler function, and
we end up with dh->filled set to 1. After seekdir(), FUSE_READDIR is
called again with a new offset, but this time the filesystem's .readdir
callback is never called, and an empty reply is returned.
Fix by setting dh->filled to 1 only when zero offsets are given to
filler function.
This commit is backported from the following commit in 'master' branch:
commit 5f125c5
Author: Rostislav <rostislav@users.noreply.github.com>
Date: Sat Jul 21 12:57:09 2018 +0300
Fix readdir() bug when a non-zero offset is specified in filler (libfuse#269)
Nikratio
pushed a commit
that referenced
this pull request
Jul 25, 2018
The bug occurs when a filesystem client reads a directory until the end,
seeks using seekdir() to some valid non-zero position and calls
readdir(). A valid 'struct dirent *' is expected, but NULL is returned
instead. Pseudocode demonstrating the bug:
DIR *dp = opendir("some_dir");
struct dirent *de = readdir(dp);
/* Get offset of the second entry */
long offset = telldir(dp);
/* Read directory until the end */
while (de)
de = readdir(de);
seekdir(dp, offset);
de = readdir(dp);
/* de must contain the second entry, but NULL is returned instead */
The reason of the bug is that when the end of directory is reached, the
kernel calls FUSE_READDIR op with an offset at the end of directory, so
the filesystem's .readdir callback never calls the filler function, and
we end up with dh->filled set to 1. After seekdir(), FUSE_READDIR is
called again with a new offset, but this time the filesystem's .readdir
callback is never called, and an empty reply is returned.
Fix by setting dh->filled to 1 only when zero offsets are given to
filler function.
This commit is backported from the following commit in 'master' branch:
commit 5f125c5
Author: Rostislav <rostislav@users.noreply.github.com>
Date: Sat Jul 21 12:57:09 2018 +0300
Fix readdir() bug when a non-zero offset is specified in filler (#269)
Merged
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Hello,
The first commit adds a test of seekdir(), and the second fixes the bug that is exposed by the test.
I am not sure this is the best fix, but I tried to change as little as possible.
Another thing is that 2.9.x branch is also affected by the same bug. Would a similar fix be accepted there as well?