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Running syzkaller with the newly enabled signed integer overflow
sanitizer produces this report:
[ 195.401651] ------------[ cut here ]------------
[ 195.404808] UBSAN: signed-integer-overflow in ../fs/open.c:321:15
[ 195.408739] 9223372036854775807 + 562984447377399 cannot be represented in type 'loff_t' (aka 'long long')
[ 195.414683] CPU: 1 PID: 703 Comm: syz-executor.0 Not tainted 6.8.0-rc2-00039-g14de58dbe653-dirty #11
[ 195.420138] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 195.425804] Call Trace:
[ 195.427360] <TASK>
[ 195.428791] dump_stack_lvl+0x93/0xd0
[ 195.431150] handle_overflow+0x171/0x1b0
[ 195.433640] vfs_fallocate+0x459/0x4f0
...
[ 195.490053] ------------[ cut here ]------------
[ 195.493146] UBSAN: signed-integer-overflow in ../fs/open.c:321:61
[ 195.497030] 9223372036854775807 + 562984447377399 cannot be represented in type 'loff_t' (aka 'long long)
[ 195.502940] CPU: 1 PID: 703 Comm: syz-executor.0 Not tainted 6.8.0-rc2-00039-g14de58dbe653-dirty #11
[ 195.508395] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 195.514075] Call Trace:
[ 195.515636] <TASK>
[ 195.517000] dump_stack_lvl+0x93/0xd0
[ 195.519255] handle_overflow+0x171/0x1b0
[ 195.521677] vfs_fallocate+0x4cb/0x4f0
[ 195.524033] __x64_sys_fallocate+0xb2/0xf0
Historically, the signed integer overflow sanitizer did not work in the
kernel due to its interaction with `-fwrapv` but this has since been
changed [1] in the newest version of Clang. It was re-enabled in the
kernel with Commit 557f8c582a9ba8ab ("ubsan: Reintroduce signed overflow
sanitizer").
Let's use the check_add_overflow helper to first verify the addition
stays within the bounds of its type (long long); then we can use that
sum for the following check.
Link: https://github.com/llvm/llvm-project/pull/82432 [1]
Closes: https://github.com/KSPP/linux/issues/356
Cc: linux-hardening@vger.kernel.org
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Justin Stitt <justinstitt@google.com>
Link: https://lore.kernel.org/r/20240513-b4-sio-vfs_fallocate-v2-1-db415872fb16@google.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
23cc6ef6fd