Jann Horn 40952b6a64 mm: enforce min addr even if capable() in expand_downwards()
commit 0a1d52994d440e21def1c2174932410b4f2a98a1 upstream.

security_mmap_addr() does a capability check with current_cred(), but
we can reach this code from contexts like a VFS write handler where
current_cred() must not be used.

This can be abused on systems without SMAP to make NULL pointer
dereferences exploitable again.

Fixes: 8869477a49c3 ("security: protect from stack expansion into low vm addresses")
Cc: stable@kernel.org
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-03-23 08:44:21 +01:00
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