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gmon: Fix allocated buffer overflow (bug 29444)

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The `__monstartup()` allocates a buffer used to store all the data
accumulated by the monitor.

The size of this buffer depends on the size of the internal structures
used and the address range for which the monitor is activated, as well
as on the maximum density of call instructions and/or callable functions
that could be potentially on a segment of executable code.

In particular a hash table of arcs is placed at the end of this buffer.
The size of this hash table is calculated in bytes as
   p->fromssize = p->textsize / HASHFRACTION;

but actually should be
   p->fromssize = ROUNDUP(p->textsize / HASHFRACTION, sizeof(*p->froms));

This results in writing beyond the end of the allocated buffer when an
added arc corresponds to a call near from the end of the monitored
address range, since `_mcount()` check the incoming caller address for
monitored range but not the intermediate result hash-like index that
uses to write into the table.

It should be noted that when the results are output to `gmon.out`, the
table is read to the last element calculated from the allocated size in
bytes, so the arcs stored outside the buffer boundary did not fall into
`gprof` for analysis. Thus this "feature" help me to found this bug
during working with https://sourceware.org/bugzilla/show_bug.cgi?id=29438

Just in case, I will explicitly note that the problem breaks the
`make test t=gmon/tst-gmon-dso` added for Bug 29438.
There, the arc of the `f3()` call disappears from the output, since in
the DSO case, the call to `f3` is located close to the end of the
monitored range.

Signed-off-by: Леонид Юрьев (Leonid Yuriev) <leo@yuriev.ru>

Another minor error seems a related typo in the calculation of
`kcountsize`, but since kcounts are smaller than froms, this is
actually to align the p->froms data.

Co-authored-by: DJ Delorie <dj@redhat.com>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
(cherry picked from commit 801af9fafd)
This commit is contained in:
Леонид Юрьев (Leonid Yuriev) 2023-02-04 14:41:38 +03:00 committed by Florian Weimer
parent 567f7413fb
commit 8e1a8e04b1
2 changed files with 4 additions and 1 deletions
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1
NEWS
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@ -127,6 +127,7 @@ The following bugs are resolved with this release:
[29305] Conserve NSS buffer space during DNS packet parsing [29305] Conserve NSS buffer space during DNS packet parsing
[29402] nscd: nscd: No such file or directory [29402] nscd: nscd: No such file or directory
[29415] nscd: Fix netlink cache invalidation if epoll is used [29415] nscd: Fix netlink cache invalidation if epoll is used
[29444] gmon: Fix allocated buffer overflow (bug 29444)
[29446] _dlopen now ignores dl_caller argument in static mode [29446] _dlopen now ignores dl_caller argument in static mode
[29490] alpha: New __brk_call implementation is broken [29490] alpha: New __brk_call implementation is broken
[29528] elf: Call __libc_early_init for reused namespaces [29528] elf: Call __libc_early_init for reused namespaces

4
gmon/gmon.c
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@ -132,6 +132,8 @@ __monstartup (u_long lowpc, u_long highpc)
p->lowpc = ROUNDDOWN(lowpc, HISTFRACTION * sizeof(HISTCOUNTER)); p->lowpc = ROUNDDOWN(lowpc, HISTFRACTION * sizeof(HISTCOUNTER));
p->highpc = ROUNDUP(highpc, HISTFRACTION * sizeof(HISTCOUNTER)); p->highpc = ROUNDUP(highpc, HISTFRACTION * sizeof(HISTCOUNTER));
p->textsize = p->highpc - p->lowpc; p->textsize = p->highpc - p->lowpc;
/* This looks like a typo, but it's here to align the p->froms
section. */
p->kcountsize = ROUNDUP(p->textsize / HISTFRACTION, sizeof(*p->froms)); p->kcountsize = ROUNDUP(p->textsize / HISTFRACTION, sizeof(*p->froms));
p->hashfraction = HASHFRACTION; p->hashfraction = HASHFRACTION;
p->log_hashfraction = -1; p->log_hashfraction = -1;
@ -142,7 +144,7 @@ __monstartup (u_long lowpc, u_long highpc)
instead of integer division. Precompute shift amount. */ instead of integer division. Precompute shift amount. */
p->log_hashfraction = ffs(p->hashfraction * sizeof(*p->froms)) - 1; p->log_hashfraction = ffs(p->hashfraction * sizeof(*p->froms)) - 1;
} }
p->fromssize = p->textsize / HASHFRACTION; p->fromssize = ROUNDUP(p->textsize / HASHFRACTION, sizeof(*p->froms));
p->tolimit = p->textsize * ARCDENSITY / 100; p->tolimit = p->textsize * ARCDENSITY / 100;
if (p->tolimit < MINARCS) if (p->tolimit < MINARCS)
p->tolimit = MINARCS; p->tolimit = MINARCS;