On 2/13/25 3:05PM, Qasim Ijaz wrote:
During the "size_check" label in ea_get(), the code checks if the extended attribute list (xattr) size matches ea_size. If not, it logs "ea_get: invalid extended attribute" and calls print_hex_dump().
Here, EALIST_SIZE(ea_buf->xattr) returns 4110417968, which exceeds INT_MAX (2,147,483,647). Then ea_size is clamped:
int size = clamp_t(int, ea_size, 0, EALIST_SIZE(ea_buf->xattr));
Although clamp_t aims to bound ea_size between 0 and 4110417968, the upper limit is treated as an int, causing an overflow above 2^31 - 1. This leads "size" to wrap around and become negative (-184549328).
The "size" is then passed to print_hex_dump() (called "len" in print_hex_dump()), it is passed as type size_t (an unsigned type), this is then stored inside a variable called "int remaining", which is then assigned to "int linelen" which is then passed to hex_dump_to_buffer(). In print_hex_dump() the for loop, iterates through 0 to len-1, where len is 18446744073525002176, calling hex_dump_to_buffer() on each iteration:
for (i = 0; i < len; i += rowsize) { linelen = min(remaining, rowsize); remaining -= rowsize;
hex_dump_to_buffer(ptr + i, linelen, rowsize, groupsize, linebuf, sizeof(linebuf), ascii);... } The expected stopping condition (i < len) is effectively broken since len is corrupted and very large. This eventually leads to the "ptr+i" being passed to hex_dump_to_buffer() to get closer to the end of the actual bounds of "ptr", eventually an out of bounds access is done in hex_dump_to_buffer() in the following for loop:
for (j = 0; j < len; j++) { if (linebuflen < lx + 2) goto overflow2; ch = ptr[j]; ... }
To fix this we should validate "EALIST_SIZE(ea_buf->xattr)" before it is utilised.
Agreed. The patch looks good. I'll add it to jfs-next
Shaggy
Reported-by: syzbot syzbot+4e6e7e4279d046613bc5@syzkaller.appspotmail.com Tested-by: syzbot syzbot+4e6e7e4279d046613bc5@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=4e6e7e4279d046613bc5 Fixes: d9f9d96136cb ("jfs: xattr: check invalid xattr size more strictly") Cc: stable@vger.kernel.org Signed-off-by: Qasim Ijaz qasdev00@gmail.com
v2:
Added Cc stable tag
fs/jfs/xattr.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/fs/jfs/xattr.c b/fs/jfs/xattr.c index 24afbae87225..7575c51cce9b 100644 --- a/fs/jfs/xattr.c +++ b/fs/jfs/xattr.c @@ -559,11 +555,16 @@ static int ea_get(struct inode *inode, struct ea_buffer *ea_buf, int min_size) size_check: if (EALIST_SIZE(ea_buf->xattr) != ea_size) {
int size = clamp_t(int, ea_size, 0, EALIST_SIZE(ea_buf->xattr));printk(KERN_ERR "ea_get: invalid extended attribute\n");print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1,ea_buf->xattr, size, 1);
if (unlikely(EALIST_SIZE(ea_buf->xattr) > INT_MAX)) {printk(KERN_ERR "ea_get: extended attribute size too large: %u > INT_MAX\n",EALIST_SIZE(ea_buf->xattr));} else {int size = clamp_t(int, ea_size, 0, EALIST_SIZE(ea_buf->xattr));printk(KERN_ERR "ea_get: invalid extended attribute\n");print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1,ea_buf->xattr, size, 1);}