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

[Qasim Ijaz <qasdev00@gmail.com>]

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")
Signed-off-by: Qasim Ijaz <qasdev00@gmail.com>
---
 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);
+		}
 		ea_release(inode, ea_buf);
 		rc = -EIO;
 		goto clean_up;
-- 
2.39.5