CVE-2024-38599

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

jffs2: prevent xattr node from overflowing the eraseblock

Add a check to make sure that the requested xattr node size is no larger than the eraseblock minus the cleanmarker.

Unlike the usual inode nodes, the xattr nodes arent split into parts and spread across multiple eraseblocks, which means that a xattr node must not occupy more than one eraseblock. If the requested xattr value is too large, the xattr node can spill onto the next eraseblock, overwriting the nodes and causing errors such as:

jffs2: argh. node added in wrong place at 0x0000b050(2) jffs2: nextblock 0x0000a000, expected at 0000b00c jffs2: error: (823) do_verify_xattr_datum: node CRC failed at 0x01e050, read=0xfc892c93, calc=0x000000 jffs2: notice: (823) jffs2_get_inode_nodes: Node header CRC failed at 0x01e00c. {848f,2fc4,0fef511f,59a3d171} jffs2: Node at 0x0000000c with length 0x00001044 would run over the end of the erase block jffs2: Perhaps the file system was created with the wrong erase size? jffs2: jffs2_scan_eraseblock(): Magic bitmask 0x1985 not found at 0x00000010: 0x1044 instead

This breaks the filesystem and can lead to KASAN crashes such as:

BUG: KASAN: slab-out-of-bounds in jffs2_sum_add_kvec+0x125e/0x15d0 Read of size 4 at addr ffff88802c31e914 by task repro/830 CPU: 0 PID: 830 Comm: repro Not tainted 6.9.0-rc3+ #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.3-1-1 04/01/2014 Call Trace: dump_stack_lvl+0xc6/0x120 print_report+0xc4/0x620 ? __virt_addr_valid+0x308/0x5b0 kasan_report+0xc1/0xf0 ? jffs2_sum_add_kvec+0x125e/0x15d0 ? jffs2_sum_add_kvec+0x125e/0x15d0 jffs2_sum_add_kvec+0x125e/0x15d0 jffs2_flash_direct_writev+0xa8/0xd0 jffs2_flash_writev+0x9c9/0xef0 ? __x64_sys_setxattr+0xc4/0x160 ? do_syscall_64+0x69/0x140 ? entry_SYSCALL_64_after_hwframe+0x76/0x7e […]

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Weakness

The product reads data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
• To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/540.html

References

• https://git.kernel.org/stable/c/2904e1d9b64f72d291095e3cbb31634f08788b11
• https://git.kernel.org/stable/c/526235dffcac74c7823ed504dfac4f88d84ba5df
• https://git.kernel.org/stable/c/8d431391320c5c5398ff966fb3a95e68a7def275
• https://git.kernel.org/stable/c/978a12c91b38bf1a213e567f3c20e2beef215f07
• https://git.kernel.org/stable/c/a1d21bcd78cf4a4353e1e835789429c6b76aca8b
• https://git.kernel.org/stable/c/af82d8d2179b7277ad627c39e7e0778f1c86ccdb
• https://git.kernel.org/stable/c/c6854e5a267c28300ff045480b5a7ee7f6f1d913
• https://git.kernel.org/stable/c/f06969df2e40ab1dc8f4364a5de967830c74a098
• https://git.kernel.org/stable/c/f0eea095ce8c959b86e1e57fe36ca4fea5ae54f8
• https://git.kernel.org/stable/c/2904e1d9b64f72d291095e3cbb31634f08788b11
• https://git.kernel.org/stable/c/526235dffcac74c7823ed504dfac4f88d84ba5df
• https://git.kernel.org/stable/c/8d431391320c5c5398ff966fb3a95e68a7def275
• https://git.kernel.org/stable/c/978a12c91b38bf1a213e567f3c20e2beef215f07
• https://git.kernel.org/stable/c/a1d21bcd78cf4a4353e1e835789429c6b76aca8b
• https://git.kernel.org/stable/c/af82d8d2179b7277ad627c39e7e0778f1c86ccdb
• https://git.kernel.org/stable/c/c6854e5a267c28300ff045480b5a7ee7f6f1d913
• https://git.kernel.org/stable/c/f06969df2e40ab1dc8f4364a5de967830c74a098
• https://git.kernel.org/stable/c/f0eea095ce8c959b86e1e57fe36ca4fea5ae54f8
• https://lists.debian.org/debian-lts-announce/2024/06/msg00020.html