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

ubifs: Fix read out-of-bounds in ubifs_wbuf_write_nolock()

Function ubifs_wbuf_write_nolock() may access buf out of bounds in following process:

ubifs_wbuf_write_nolock(): aligned_len = ALIGN(len, 8); // Assume len = 4089, aligned_len = 4096 if (aligned_len <= wbuf->avail) … // Not satisfy if (wbuf->used) { ubifs_leb_write() // Fill some data in avail wbuf len -= wbuf->avail; // len is still not 8-bytes aligned aligned_len -= wbuf->avail; } n = aligned_len » c->max_write_shift; if (n) { n «= c->max_write_shift; err = ubifs_leb_write(c, wbuf->lnum, buf + written, wbuf->offs, n); // n > len, read out of bounds less than 8(n-len) bytes }

, which can be catched by KASAN:

BUG: KASAN: slab-out-of-bounds in ecc_sw_hamming_calculate+0x1dc/0x7d0 Read of size 4 at addr ffff888105594ff8 by task kworker/u8:4/128 Workqueue: writeback wb_workfn (flush-ubifs_0_0) Call Trace: kasan_report.cold+0x81/0x165 nand_write_page_swecc+0xa9/0x160 ubifs_leb_write+0xf2/0x1b0 [ubifs] ubifs_wbuf_write_nolock+0x421/0x12c0 [ubifs] write_head+0xdc/0x1c0 [ubifs] ubifs_jnl_write_inode+0x627/0x960 [ubifs] wb_workfn+0x8af/0xb80

Function ubifs_wbuf_write_nolock() accepts that parameter len is not 8 bytes aligned, the len represents the true length of buf (which is allocated in ubifs_jnl_xxx, eg. ubifs_jnl_write_inode), so ubifs_wbuf_write_nolock() must handle the length read from buf carefully to write leb safely.

Fetch a reproducer in [Link].

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/07a209fadee7b53b46858538e1177597273862e4
• https://git.kernel.org/stable/c/3b7fb89135a20587d57f8877c02e25003e9edbdf
• https://git.kernel.org/stable/c/4f2262a334641e05f645364d5ade1f565c85f20b
• https://git.kernel.org/stable/c/5343575aa11c5d7044107d59d43f84aec01312b0
• https://git.kernel.org/stable/c/a7054aaf1909cf40489c0ec1b728fdcf79c751a6
• https://git.kernel.org/stable/c/b80ccbec0e4804436c382d7dd60e943c386ed83a
• https://git.kernel.org/stable/c/e09fa5318d51f522e1af4fbaf8f74999355980c8