usdt: use ProcMountNSGuard for pid and path attach #2064
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Since the probe may be in a descendent namespace, ensure that when `stat()`ing for HINTs and resolving linked elf locations, be sure to always perform them relative to any observed mount namespace. However, usage of the mount namespace must be surgical, since we're observing the pid with its outter identity, make sure we're not in the mount namespace when attempting to `readlink` the `/proc/<pid>/exe`
tjfontaine
requested review from
4ast,
drzaeus77 and
yonghong-song
as code owners
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[buildbot, test this please] |
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@palmtenor could you help check the patch as well? currently, we have some mount related tests at |
| ProcMountNSGuard g(new ProcMountNS(pid)); | ||
| struct stat buffer; | ||
| if (strlen(path) >= 1 && path[0] != '/') { | ||
| fprintf(stderr, "HINT: Binary path should be absolute.\n\n"); |
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Well, I personally have used say trace.py u:./somebinary:tracePoint --pid PID. If the target Process is in global namespace this would actually work. Maybe just add a hint if the actual context construction failed and say this might be the reason, instead of just directly fail?
Good observation. |
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What is still outstanding to merge this? Ran into the same issues as @tjfontaine when looking at usdt support in bpftrace, and discovered that bcc itself doesn't properly handle mount namespaces for its own path check, which this seems to fix. |
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Let us merge this then. |
Since the probe may be in a descendent namespace, ensure that when `stat()`ing for HINTs and resolving linked elf locations, be sure to always perform them relative to any observed mount namespace. However, usage of the mount namespace must be surgical, since we're observing the pid with its outter identity, make sure we're not in the mount namespace when attempting to `readlink` the `/proc/<pid>/exe`
Since the probe may be in a descendent namespace, ensure that when `stat()`ing for HINTs and resolving linked elf locations, be sure to always perform them relative to any observed mount namespace. However, usage of the mount namespace must be surgical, since we're observing the pid with its outter identity, make sure we're not in the mount namespace when attempting to `readlink` the `/proc/<pid>/exe`
This adds a couple of lexical scopes for usage with
ProcMountNSGuardso the hint'ing works for the C interface when usingbcc_usdt_new_frompid(). Also, add a guard for theContext::Context(pid, path)constructor for resolving the probes.From the commit message:
Since the probe may be in a descendent namespace, ensure that when
stat()ing for HINTs and resolving linked elf locations, be sure to always perform them relative to any observed mount namespace.However, usage of the mount namespace must be surgical, since we're observing the pid with its outter identity, make sure we're not in the mount namespace when attempting to
readlinkthe/proc/<pid>/exe