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An overread condition in memccpy(dst, src, c, len) would occur if
src does not cross a 16 byte boundary and there is no instance of
c between *src and the next 16 byte boundary. This could cause a
read fault if src is just before the end of a page and the next page
is unmapped or unreadable.
The bug is a consequence of basing memccpy() on the strlcpy() code:
whereas strlcpy() assumes that src is a nul-terminated string and
hence a terminator is always present, c may not be present at all in
the source string. It was not caught earlier due to insufficient
unit test design.
As a part of the fix, the function is refactored such that the runt
case (buffer length from last alignment boundary between 1 and 32 B)
is handled separately. This reduces the number of conditional
branches on all code paths and simplifies the handling of early
matches in the non-runt case. Performance is improved slightly.
os: FreeBSD
arch: amd64
cpu: 11th Gen Intel(R) Core(TM) i7-1165G7 @ 2.80GHz
│ memccpy.unfixed.out │ memccpy.fixed.out │
│ sec/op │ sec/op vs base │
Short 66.76µ ± 0% 62.45µ ± 1% -6.44% (p=0.000 n=20)
Mid 7.938µ ± 0% 7.967µ ± 0% +0.36% (p=0.001 n=20)
Long 3.577µ ± 0% 3.577µ ± 0% ~ (p=0.429 n=20)
geomean 12.38µ 12.12µ -2.08%
│ memccpy.unfixed.out │ memccpy.fixed.out │
│ B/s │ B/s vs base │
Short 1.744Gi ± 0% 1.864Gi ± 1% +6.89% (p=0.000 n=20)
Mid 14.67Gi ± 0% 14.61Gi ± 0% -0.36% (p=0.001 n=20)
Long 32.55Gi ± 0% 32.55Gi ± 0% ~ (p=0.429 n=20)
geomean 9.407Gi 9.606Gi +2.12%
Reported by: getz
Reviewed by: getz
Approved by: mjg (blanket, via IRC)
See also: D46051
MFC: stable/14
Event: GSoC 2024
Differential Revision: https://reviews.freebsd.org/D46052
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| .. | ||
| aarch64 | ||
| amd64 | ||
| arm | ||
| capability | ||
| compat-43 | ||
| csu | ||
| db | ||
| gdtoa | ||
| gen | ||
| gmon | ||
| i386 | ||
| iconv | ||
| include | ||
| inet | ||
| isc | ||
| locale | ||
| md | ||
| nameser | ||
| net | ||
| nls | ||
| posix1e | ||
| powerpc | ||
| powerpc64 | ||
| powerpcspe | ||
| quad | ||
| regex | ||
| resolv | ||
| riscv | ||
| rpc | ||
| secure | ||
| softfloat | ||
| stdio | ||
| stdlib | ||
| stdtime | ||
| string | ||
| sys | ||
| tests | ||
| uuid | ||
| x86/gen | ||
| xdr | ||
| yp | ||
| libc.ldscript | ||
| libc_nossp.ldscript | ||
| Makefile | ||
| Makefile.depend | ||
| Makefile.depend.options | ||
| Versions.def | ||