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Kees Cook authored
commit 98da7d08 upstream. When limiting the argv/envp strings during exec to 1/4 of the stack limit, the storage of the pointers to the strings was not included. This means that an exec with huge numbers of tiny strings could eat 1/4 of the stack limit in strings and then additional space would be later used by the pointers to the strings. For example, on 32-bit with a 8MB stack rlimit, an exec with 1677721 single-byte strings would consume less than 2MB of stack, the max (8MB / 4) amount allowed, but the pointers to the strings would consume the remaining additional stack space (1677721 * 4 == 6710884). The result (1677721 + 6710884 == 8388605) would exhaust stack space entirely. Controlling this stack exhaustion could result in pathological behavior in setuid binaries (CVE-2017-1000365). [akpm@linux-foundation.org: additional commenting from Kees] Fixes: b6a2fea3 ("mm: variable length argument support") Link: http://lkml.kernel.org/r/20170622001720.GA32173@beastSigned-off-by:
Kees Cook <keescook@chromium.org> Acked-by:
Rik van Riel <riel@redhat.com> Acked-by:
Michal Hocko <mhocko@suse.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Qualys Security Advisory <qsa@qualys.com> Signed-off-by:
Andrew Morton <akpm@linux-foundation.org> Signed-off-by:
Linus Torvalds <torvalds@linux-foundation.org> [bwh: Backported to 3.16: use ACCESS_ONCE() instead of READ_ONCE()] Signed-off-by:
Ben Hutchings <ben@decadent.org.uk>
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