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From 6d3e97e83a7d61cbb2f5109efb4b519383a55712 Mon Sep 17 00:00:00 2001
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From: Eugene Syromyatnikov <evgsyr@gmail.com>
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Date: Tue, 28 Jun 2022 16:55:49 +0200
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Subject: [PATCH] util: add offs sanity check to print_clock_t
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While it is not strictly needed right now, the code that uses
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the calculated offs value lacks any checks for possible buf overruns,
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which is not defensive enough, so let's add them. Reported by covscan:
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Error: OVERRUN (CWE-119):
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strace-5.18/src/util.c:248: assignment: Assigning:
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"offs" = "ilog10(val / clk_tck)". The value of "offs" is now between
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16 and 31 (inclusive).
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strace-5.18/src/util.c:249: overrun-local: Overrunning array of 30 bytes
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at byte offset 31 by dereferencing pointer "buf + offs". [Note: The source
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code implementation of the function has been overridden by a builtin model.]
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Error: OVERRUN (CWE-119):
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strace-5.18/src/util.c:248: assignment: Assigning:
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"offs" = "ilog10(val / clk_tck)". The value of "offs" is now between
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16 and 31 (inclusive).
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strace-5.18/src/util.c:253: overrun-buffer-arg: Overrunning array "buf"
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of 30 bytes by passing it to a function which accesses it at byte offset
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32 using argument "offs + 2UL" (which evaluates to 33). [Note: The source
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code implementation of the function has been overridden by a builtin model.]
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Error: OVERRUN (CWE-119):
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strace-5.18/src/util.c:248: assignment: Assigning:
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"offs" = "ilog10(val / clk_tck)". The value of "offs" is now between
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16 and 31 (inclusive).
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strace-5.18/src/util.c:254: overrun-local: Overrunning array "buf"
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of 30 bytes at byte offset 32 using index "offs + 1UL" (which evaluates
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to 32).
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* src/util.c (print_clock_t): Add check that offs is small enough
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for it and "offs + 2" not to overrun buf.
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---
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src/util.c | 8 ++++++++
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1 file changed, 8 insertions(+)
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diff --git a/src/util.c b/src/util.c
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index 5f87acb..93aa7b3 100644
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--- a/src/util.c
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+++ b/src/util.c
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@@ -246,6 +246,14 @@ print_clock_t(uint64_t val)
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*/
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char buf[sizeof(uint64_t) * 3 + sizeof("0.0 s")];
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size_t offs = ilog10(val / clk_tck);
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+ /*
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+ * This check is mostly to appease covscan, which thinks
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+ * that offs can go as high as 31 (it cannot), but since
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+ * there is no proper sanity checks against offs overrunning
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+ * buf down the code, it may as well be here.
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+ */
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+ if (offs > (sizeof(buf) - sizeof("0.0 s")))
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+ return;
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int ret = snprintf(buf + offs, sizeof(buf) - offs, "%.*f s",
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frac_width,
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(double) (val % clk_tck) / clk_tck);
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--
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2.1.4
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