jfs: fix slab-out-of-bounds read in ea_get()

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 <[e-mail]>
Tested-by: syzbot <[e-mail]>
Closes: https://syzkaller.appspot.com/bug?extid=4e6e7e4279d046613bc5
Fixes: d9f9d96136cb ("jfs: xattr: check invalid xattr size more strictly")
Cc: [e-mail]
Signed-off-by: Qasim Ijaz <[e-mail]>
Signed-off-by: Dave Kleikamp <[e-mail]>

fs/jfs/xattr.c

···
 
       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;