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Subject[PATCH] fs/exec: Test patch for syzkaller crash
Date
From: Ira Weiny <ira.weiny@intel.com>

Kees reported that it looked like the kmap_local_page() conversion in
fs/exec.c was causing a crash with the syzkaller.[1]

At first glance it appeared this was due to the lack of pagefaults not
being disabled as was done by kmap_atomic().

Unfortunately, after deeper investigation we don't see how this is a
problem. The crash does not appear to be happening in the
memcpy_to_page() call.[2]

For testing, add back pagefault disable in copy_string_kernel() to see
if it makes syzkaller happy. If so more investigation will need to be
done to understand exactly what is happening.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c6e8e36c6ae4b11bed5643317afb66b6c3cadba8
[2] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/fs/exec.c?id=40d43a7507e1547dd45cb02af2e40d897c591870#n616

Cc: Kees Cook <keescook@chromium.org>
Reported-by: syzbot+3250d9c8925ef29e975f@syzkaller.appspotmail.com
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
---
fs/exec.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/fs/exec.c b/fs/exec.c
index b51dd14e7388..e076b228123a 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -640,7 +640,9 @@ int copy_string_kernel(const char *arg, struct linux_binprm *bprm)
if (!page)
return -E2BIG;
flush_arg_page(bprm, pos & PAGE_MASK, page);
+ pagefault_disable();
memcpy_to_page(page, offset_in_page(pos), arg, bytes_to_copy);
+ pagefault_enable();
put_arg_page(page);
}

--
2.35.3
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