CVE-2025-39735

In the Linux kernel, the following vulnerability has been resolved:

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.

This vulnerability is rated Moderate because triggering the out-of-bounds read requires the ability to mount a maliciously structured filesystem image, limiting the attack surface to a local denial of service or potential kernel memory disclosure. In standard Red Hat Enterprise Linux deployments, mounting arbitrary storage media requires administrative privileges such as CAP_SYS_ADMIN. Furthermore, the legacy JFS filesystem is not enabled or utilized in typical enterprise configurations, significantly reducing overall exposure.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.