{"id":"CVE-2021-47608","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix kernel address leakage in atomic fetch\n\nThe change in commit 37086bfdc737 (\"bpf: Propagate stack bounds to registers\nin atomics w/ BPF_FETCH\") around check_mem_access() handling is buggy since\nthis would allow for unprivileged users to leak kernel pointers. For example,\nan atomic fetch/and with -1 on a stack destination which holds a spilled\npointer will migrate the spilled register type into a scalar, which can then\nbe exported out of the program (since scalar != pointer) by dumping it into\na map value.\n\nThe original implementation of XADD was preventing this situation by using\na double call to check_mem_access() one with BPF_READ and a subsequent one\nwith BPF_WRITE, in both cases passing -1 as a placeholder value instead of\nregister as per XADD semantics since it didn't contain a value fetch. The\nBPF_READ also included a check in check_stack_read_fixed_off() which rejects\nthe program if the stack slot is of __is_pointer_value() if dst_regno \u003c 0.\nThe latter is to distinguish whether we're dealing with a regular stack spill/\nfill or some arithmetical operation which is disallowed on non-scalars, see\nalso 6e7e63cbb023 (\"bpf: Forbid XADD on spilled pointers for unprivileged\nusers\") for more context on check_mem_access() and its handling of placeholder\nvalue -1.\n\nOne minimally intrusive option to fix the leak is for the BPF_FETCH case to\ninitially check the BPF_READ case via check_mem_access() with -1 as register,\nfollowed by the actual load case with non-negative load_reg to propagate\nstack bounds to registers.","modified":"2026-03-14T01:39:30.436898Z","published":"2024-06-19T15:15:55.360Z","related":["SUSE-SU-2024:2372-1","SUSE-SU-2024:2394-1","SUSE-SU-2024:2902-1","SUSE-SU-2024:2929-1","SUSE-SU-2024:2939-1"],"references":[{"type":"FIX","url":"https://git.kernel.org/stable/c/423628125a484538111c2c6d9bb1588eb086053b"},{"type":"FIX","url":"https://git.kernel.org/stable/c/7d3baf0afa3aa9102d6a521a8e4c41888bb79882"}],"affected":[{"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2021-47608.json","unresolved_ranges":[{"events":[{"introduced":"5.12"},{"fixed":"5.15.11"}]},{"events":[{"introduced":"0"},{"last_affected":"5.16-rc1"}]},{"events":[{"introduced":"0"},{"last_affected":"5.16-rc2"}]},{"events":[{"introduced":"0"},{"last_affected":"5.16-rc3"}]},{"events":[{"introduced":"0"},{"last_affected":"5.16-rc4"}]},{"events":[{"introduced":"0"},{"last_affected":"5.16-rc5"}]}]}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N"}]}