udf_symlink_filler() can enter udf_pc_to_char() with a partial pathComponent header.

Validate that enough input remains for a complete pathComponent header
before accessing it. Reject malformed symlink data that would otherwise
make udf_pc_to_char() perform an out-of-bounds read.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: David Lee <david.lee@trailofbits.com>
Assisted-by: Codex:gpt-5.5
---
Trail of Bits has a reproducer that triggers a kernel panic demonstrating
this bug and can share it if needed.

fs/udf/symlink.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/udf/symlink.c b/fs/udf/symlink.c
index fe03745..a05d188 100644
--- a/fs/udf/symlink.c
+++ b/fs/udf/symlink.c
@@ -36,6 +36,8 @@ static int udf_pc_to_char(struct super_block *sb, unsigned char *from,
 	/* Reserve one byte for terminating \0 */
 	tolen--;
 	while (elen < fromlen) {
+		if (fromlen - elen < sizeof(struct pathComponent))
+			return -EIO;
 		pc = (struct pathComponent *)(from + elen);
 		elen += sizeof(struct pathComponent);
 		switch (pc->componentType) {

On Fri 17-07-26 10:47:21, David Lee wrote:
> udf_symlink_filler() can enter udf_pc_to_char() with a partial pathComponent header.
> 
> Validate that enough input remains for a complete pathComponent header
> before accessing it. Reject malformed symlink data that would otherwise
> make udf_pc_to_char() perform an out-of-bounds read.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: David Lee <david.lee@trailofbits.com>
> Assisted-by: Codex:gpt-5.5

Thanks! I've added the patch to my tree.

								Honza

> ---
> Trail of Bits has a reproducer that triggers a kernel panic demonstrating
> this bug and can share it if needed.
> 
> fs/udf/symlink.c |    2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/udf/symlink.c b/fs/udf/symlink.c
> index fe03745..a05d188 100644
> --- a/fs/udf/symlink.c
> +++ b/fs/udf/symlink.c
> @@ -36,6 +36,8 @@ static int udf_pc_to_char(struct super_block *sb, unsigned char *from,
>  	/* Reserve one byte for terminating \0 */
>  	tolen--;
>  	while (elen < fromlen) {
> +		if (fromlen - elen < sizeof(struct pathComponent))
> +			return -EIO;
>  		pc = (struct pathComponent *)(from + elen);
>  		elen += sizeof(struct pathComponent);
>  		switch (pc->componentType) {
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR