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71 lines
3.2 KiB
71 lines
3.2 KiB
1 year ago
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commit 801af9fafd4689337ebf27260aa115335a0cb2bc
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Author: Леонид Юрьев (Leonid Yuriev) <leo@yuriev.ru>
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Date: Sat Feb 4 14:41:38 2023 +0300
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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
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accumulated by the monitor.
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The size of this buffer depends on the size of the internal structures
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used and the address range for which the monitor is activated, as well
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as on the maximum density of call instructions and/or callable functions
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that could be potentially on a segment of executable code.
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In particular a hash table of arcs is placed at the end of this buffer.
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The size of this hash table is calculated in bytes as
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p->fromssize = p->textsize / HASHFRACTION;
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but actually should be
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p->fromssize = ROUNDUP(p->textsize / HASHFRACTION, sizeof(*p->froms));
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This results in writing beyond the end of the allocated buffer when an
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added arc corresponds to a call near from the end of the monitored
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address range, since `_mcount()` check the incoming caller address for
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monitored range but not the intermediate result hash-like index that
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uses to write into the table.
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It should be noted that when the results are output to `gmon.out`, the
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table is read to the last element calculated from the allocated size in
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bytes, so the arcs stored outside the buffer boundary did not fall into
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`gprof` for analysis. Thus this "feature" help me to found this bug
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during working with https://sourceware.org/bugzilla/show_bug.cgi?id=29438
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Just in case, I will explicitly note that the problem breaks the
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`make test t=gmon/tst-gmon-dso` added for Bug 29438.
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There, the arc of the `f3()` call disappears from the output, since in
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the DSO case, the call to `f3` is located close to the end of the
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monitored range.
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Signed-off-by: Леонид Юрьев (Leonid Yuriev) <leo@yuriev.ru>
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Another minor error seems a related typo in the calculation of
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`kcountsize`, but since kcounts are smaller than froms, this is
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actually to align the p->froms data.
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Co-authored-by: DJ Delorie <dj@redhat.com>
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Reviewed-by: Carlos O'Donell <carlos@redhat.com>
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diff --git a/gmon/gmon.c b/gmon/gmon.c
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index dee64803ada583d7..bf76358d5b1aa2da 100644
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--- a/gmon/gmon.c
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+++ b/gmon/gmon.c
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@@ -132,6 +132,8 @@ __monstartup (u_long lowpc, u_long highpc)
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p->lowpc = ROUNDDOWN(lowpc, HISTFRACTION * sizeof(HISTCOUNTER));
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p->highpc = ROUNDUP(highpc, HISTFRACTION * sizeof(HISTCOUNTER));
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p->textsize = p->highpc - p->lowpc;
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+ /* This looks like a typo, but it's here to align the p->froms
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+ section. */
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p->kcountsize = ROUNDUP(p->textsize / HISTFRACTION, sizeof(*p->froms));
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p->hashfraction = HASHFRACTION;
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p->log_hashfraction = -1;
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@@ -142,7 +144,7 @@ __monstartup (u_long lowpc, u_long highpc)
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instead of integer division. Precompute shift amount. */
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p->log_hashfraction = ffs(p->hashfraction * sizeof(*p->froms)) - 1;
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}
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- p->fromssize = p->textsize / HASHFRACTION;
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+ p->fromssize = ROUNDUP(p->textsize / HASHFRACTION, sizeof(*p->froms));
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p->tolimit = p->textsize * ARCDENSITY / 100;
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if (p->tolimit < MINARCS)
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p->tolimit = MINARCS;
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