string: Fix OOB read on generic strncmp
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| dj/TryBot-apply_patch |
success
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Patch applied to master at the time it was sent
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| dj/TryBot-32bit |
success
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Build for i686
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Commit Message
For unaligned case, reading ahead can only be done if parting reads
matches the aligned input.
Also extend the stratcliff tests to check such cases.
Checked on x86_64-linux-gnu, i686-linux-gnu, powerpc64-linux-gnu,
and powerpc-linux-gnu by removing the arch-specific assembly
implementation and disabling multi-arch (it covers both LE and BE
for 64 and 32 bits).
---
string/stratcliff.c | 17 +++++++++++++++++
string/strncmp.c | 13 ++++++++++++-
2 files changed, 29 insertions(+), 1 deletion(-)
Comments
The 02/21/2023 16:06, Adhemerval Zanella wrote:
> For unaligned case, reading ahead can only be done if parting reads
> matches the aligned input.
>
> Also extend the stratcliff tests to check such cases.
>
> Checked on x86_64-linux-gnu, i686-linux-gnu, powerpc64-linux-gnu,
> and powerpc-linux-gnu by removing the arch-specific assembly
> implementation and disabling multi-arch (it covers both LE and BE
> for 64 and 32 bits).
> ---
> string/stratcliff.c | 17 +++++++++++++++++
> string/strncmp.c | 13 ++++++++++++-
> 2 files changed, 29 insertions(+), 1 deletion(-)
>
> diff --git a/string/stratcliff.c b/string/stratcliff.c
> index 74d64cc03d..864d856921 100644
> --- a/string/stratcliff.c
> +++ b/string/stratcliff.c
> @@ -409,6 +409,23 @@ do_test (void)
> }
> }
>
> + for (outer = 1; outer < 32; ++outer)
> + for (middle = 0; middle < 16; ++middle)
> + {
> + MEMSET (adr + middle, L('T'), 256);
> + adr[256] = L('\0');
> + MEMSET (dest + nchars - outer, L('T'), outer - 1);
> + dest[nchars - outer] = L('U');
> +
> + if (STRNCMP (adr + middle, &dest[nchars - middle - 1], outer) > 0)
> + {
> + printf ("%s 1 flunked for outer = %zu, middle = %zu, "
> + "inner = %zu\n",
> + STRINGIFY (STRNCMP), outer, middle, inner);
> + result = 1;
> + }
> + }
> +
this depends on dest[nchars-1] != 'T' when outer > middle+1
and dest[nchars-middle-1] <= 'T' when outer < middle
which is not clear from the context.
below the existing
if (STRNCMP (adr + middle, dest + nchars - outer, outer) >= 0) ...
i'd just add
if (STRNCMP (adr + middle, dest + nchars - outer, outer + 99) >= 0) ...
and then with flipped args too.
> diff --git a/string/strncmp.c b/string/strncmp.c
> index 4c8bf36bb9..751bf53d55 100644
> --- a/string/strncmp.c
> +++ b/string/strncmp.c
> @@ -73,7 +73,11 @@ strncmp_unaligned_loop (const op_t *x1, const op_t *x2, op_t w1, uintptr_t ofs,
> uintptr_t sh_2 = sizeof(op_t) * CHAR_BIT - sh_1;
>
> op_t w2 = MERGE (w2a, sh_1, (op_t)-1, sh_2);
> - if (!has_zero (w2) && n > (sizeof (op_t) - ofs))
> +
> + /* Reading ahead is wrong if w1 and w2 already differs. */
> + op_t w1a = MERGE (w1, 0, (op_t)-1, sh_2);
> +
> + if (!has_zero (w2) && w2 == w1a && n >= (sizeof (op_t) - ofs))
> {
> op_t w2b;
>
> @@ -90,6 +94,13 @@ strncmp_unaligned_loop (const op_t *x1, const op_t *x2, op_t w1, uintptr_t ofs,
> if (has_zero (w2b) || n <= (sizeof (op_t) - ofs))
> break;
> w1 = *x1++;
> +
> + /* Reading ahead is wrong if w1 and w2 already differs. */
> + w2 = MERGE (w2b, sh_1, (op_t)-1, sh_2);
> + w1a = MERGE (w1, 0, (op_t)-1, sh_2);
> + if (w2 != w1a)
> + return final_cmp (w1a, w2, n);
> +
> w2a = w2b;
> }
i have difficulty following this code, but it looks ok to me.
@@ -409,6 +409,23 @@ do_test (void)
}
}
+ for (outer = 1; outer < 32; ++outer)
+ for (middle = 0; middle < 16; ++middle)
+ {
+ MEMSET (adr + middle, L('T'), 256);
+ adr[256] = L('\0');
+ MEMSET (dest + nchars - outer, L('T'), outer - 1);
+ dest[nchars - outer] = L('U');
+
+ if (STRNCMP (adr + middle, &dest[nchars - middle - 1], outer) > 0)
+ {
+ printf ("%s 1 flunked for outer = %zu, middle = %zu, "
+ "inner = %zu\n",
+ STRINGIFY (STRNCMP), outer, middle, inner);
+ result = 1;
+ }
+ }
+
/* strncpy/wcsncpy tests */
adr[nchars - 1] = L('T');
for (outer = nchars; outer >= max128; --outer)
@@ -73,7 +73,11 @@ strncmp_unaligned_loop (const op_t *x1, const op_t *x2, op_t w1, uintptr_t ofs,
uintptr_t sh_2 = sizeof(op_t) * CHAR_BIT - sh_1;
op_t w2 = MERGE (w2a, sh_1, (op_t)-1, sh_2);
- if (!has_zero (w2) && n > (sizeof (op_t) - ofs))
+
+ /* Reading ahead is wrong if w1 and w2 already differs. */
+ op_t w1a = MERGE (w1, 0, (op_t)-1, sh_2);
+
+ if (!has_zero (w2) && w2 == w1a && n >= (sizeof (op_t) - ofs))
{
op_t w2b;
@@ -90,6 +94,13 @@ strncmp_unaligned_loop (const op_t *x1, const op_t *x2, op_t w1, uintptr_t ofs,
if (has_zero (w2b) || n <= (sizeof (op_t) - ofs))
break;
w1 = *x1++;
+
+ /* Reading ahead is wrong if w1 and w2 already differs. */
+ w2 = MERGE (w2b, sh_1, (op_t)-1, sh_2);
+ w1a = MERGE (w1, 0, (op_t)-1, sh_2);
+ if (w2 != w1a)
+ return final_cmp (w1a, w2, n);
+
w2a = w2b;
}