[PATCH 5.4 153/154] jfs: fix slab-out-of-bounds read in ea_get()

Greg Kroah-Hartman
2025-04-08T12:09:30Z

From: Qasim Ijaz <qasdev00@gmail.com>

commit fdf480da5837c23b146c4743c18de97202fcab37 upstream.

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.

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>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/jfs/xattr.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

--- a/fs/jfs/xattr.c
+++ b/fs/jfs/xattr.c
@@ -559,11 +559,16 @@ static int ea_get(struct inode *inode, s

size_check:
if (EALIST_SIZE(ea_buf->xattr) != ea_size) {
- int size = clamp_t(int, ea_size, 0, EALIST_SIZE(ea_buf->xattr));
+ 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);
+ printk(KERN_ERR "ea_get: invalid extended attribute\n");
+ print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1,
+ ea_buf->xattr, size, 1);
+ }
ea_release(inode, ea_buf);
rc = -EIO;
goto clean_up;