From: Justin Stitt <justinstitt@xxxxxxxxxx>
[ Upstream commit 23cc6ef6fd453b13502caae23130844e7d6ed0fe ]
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@xxxxxxxxxxxxxxx
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240513-b4-sio-vfs_fallocate-v2-1-db415872fb16@xxxxxxxxxx
Reviewed-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
fs/open.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/fs/open.c b/fs/open.c
index f1c2ec6790bb3..d88b7f3b4d9f1 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -230,6 +230,7 @@ int vfs_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
{
struct inode *inode = file_inode(file);
long ret;
+ loff_t sum;
if (offset < 0 || len <= 0)
return -EINVAL;
@@ -298,8 +299,11 @@ int vfs_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
if (!S_ISREG(inode->i_mode) && !S_ISBLK(inode->i_mode))
return -ENODEV;
- /* Check for wrap through zero too */
- if (((offset + len) > inode->i_sb->s_maxbytes) || ((offset + len) < 0))
+ /* Check for wraparound */
+ if (check_add_overflow(offset, len, &sum))
+ return -EFBIG;
+
+ if (sum > inode->i_sb->s_maxbytes)
return -EFBIG;
if (!file->f_op->fallocate)
--
2.43.0
