Bug 2360930 (CVE-2025-39735) - CVE-2025-39735 kernel: jfs: fix slab-out-of-bounds read in ea_get()
Summary: CVE-2025-39735 kernel: jfs: fix slab-out-of-bounds read in ea_get()
Keywords:
Status: NEW
Alias: CVE-2025-39735
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
medium
medium
Target Milestone: ---
Assignee: Product Security DevOps Team
QA Contact:
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2025-04-18 08:01 UTC by OSIDB Bzimport
Modified: 2025-04-18 14:37 UTC (History)
4 users (show)

Fixed In Version:
Clone Of:
Environment:
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Description OSIDB Bzimport 2025-04-18 08:01:43 UTC
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.

Comment 1 Avinash Hanwate 2025-04-18 13:04:33 UTC
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025041820-CVE-2025-39735-41c8@gregkh/T


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