Messages in this thread Patch in this message | | | From | Eryu Guan <> | Subject | [PATCH] lib/string: avoid reading beyond src buffer in strscpy | Date | Thu, 7 Dec 2017 19:33:24 +0800 |
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strscpy() tries to copy sizeof(unsigned long) bytes a time from src to dest when possible, and stops the loop when 'max' is less than sizeof(unsigned long). But it doesn't check if (src+res) goes beyond src buffer and does out-of-bound access to the underlying memory.
KASAN reported global-out-of-bound bug when reading seccomp actions_logged file in procfs:
cat /proc/sys/kernel/seccomp/actions_logged
Because seccomp_names_from_actions_logged() is copying short strings (less than sizeof(unsigned long)) to buffer 'names'. e.g.
ret = strscpy(names, " ", size);
Fixed by capping the 'max' value according to the src buffer size, to make sure we won't go beyond src buffer.
Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Chris Metcalf <cmetcalf@ezchip.com> Cc: Kees Cook <keescook@chromium.org> Signed-off-by: Eryu Guan <eguan@redhat.com> --- lib/string.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/lib/string.c b/lib/string.c index 64a9e33f1daa..13a0147eea00 100644 --- a/lib/string.c +++ b/lib/string.c @@ -179,6 +179,7 @@ ssize_t strscpy(char *dest, const char *src, size_t count) { const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; size_t max = count; + size_t src_sz = strlen(src) + 1; long res = 0; if (count == 0) @@ -200,6 +201,10 @@ ssize_t strscpy(char *dest, const char *src, size_t count) max = 0; #endif + /* avoid reading beyond src buffer */ + if (max > src_sz) + max = src_sz; + while (max >= sizeof(unsigned long)) { unsigned long c, data; -- 2.14.3
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