From: Sai Ritvik Tanksalkar <stanksal@purdue.edu> stable inclusion from stable-v6.6.128 commit cff0ef043e16feb5a02307c8f9d0117a96c5587c category: bugfix bugzilla: https://atomgit.com/openeuler/kernel/issues/8792 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- [ Upstream commit 5669645c052f235726a85f443769b6fc02f66762 ] persistent_ram_save_old() can be called multiple times for the same persistent_ram_zone (e.g., via ramoops_pstore_read -> ramoops_get_next_prz for PSTORE_TYPE_DMESG records). Currently, the function only allocates prz->old_log when it is NULL, but it unconditionally updates prz->old_log_size to the current buffer size and then performs memcpy_fromio() using this new size. If the buffer size has grown since the first allocation (which can happen across different kernel boot cycles), this leads to: 1. A heap buffer overflow (OOB write) in the memcpy_fromio() calls 2. A subsequent OOB read when ramoops_pstore_read() accesses the buffer using the incorrect (larger) old_log_size The KASAN splat would look similar to: BUG: KASAN: slab-out-of-bounds in ramoops_pstore_read+0x... Read of size N at addr ... by task ... The conditions are likely extremely hard to hit: 0. Crash with a ramoops write of less-than-record-max-size bytes. 1. Reboot: ramoops registers, pstore_get_records(0) reads old crash, allocates old_log with size X 2. Crash handler registered, timer started (if pstore_update_ms >= 0) 3. Oops happens (non-fatal, system continues) 4. pstore_dump() writes oops via ramoops_pstore_write() size Y (>X) 5. pstore_new_entry = 1, pstore_timer_kick() called 6. System continues running (not a panic oops) 7. Timer fires after pstore_update_ms milliseconds 8. pstore_timefunc() → schedule_work() → pstore_dowork() → pstore_get_records(1) 9. ramoops_get_next_prz() → persistent_ram_save_old() 10. buffer_size() returns Y, but old_log is X bytes 11. Y > X: memcpy_fromio() overflows heap Requirements: - a prior crash record exists that did not fill the record size (almost impossible since the crash handler writes as much as it can possibly fit into the record, capped by max record size and the kmsg buffer almost always exceeds the max record size) - pstore_update_ms >= 0 (disabled by default) - Non-fatal oops (system survives) Free and reallocate the buffer when the new size differs from the previously allocated size. This ensures old_log always has sufficient space for the data being copied. Fixes: 201e4aca5aa1 ("pstore/ram: Should update old dmesg buffer before reading") Signed-off-by: Sai Ritvik Tanksalkar <stanksal@purdue.edu> Link: https://patch.msgid.link/20260201132240.2948732-1-stanksal@purdue.edu Signed-off-by: Kees Cook <kees@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Yuan can <yuancan@huawei.com> Signed-off-by: Pan Taixi <pantaixi1@huawei.com> --- fs/pstore/ram_core.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c index f1848cdd6d34..c9eaacdec37e 100644 --- a/fs/pstore/ram_core.c +++ b/fs/pstore/ram_core.c @@ -298,6 +298,17 @@ void persistent_ram_save_old(struct persistent_ram_zone *prz) if (!size) return; + /* + * If the existing buffer is differently sized, free it so a new + * one is allocated. This can happen when persistent_ram_save_old() + * is called early in boot and later for a timer-triggered + * survivable crash when the crash dumps don't match in size + * (which would be extremely unlikely given kmsg buffers usually + * exceed prz buffer sizes). + */ + if (prz->old_log && prz->old_log_size != size) + persistent_ram_free_old(prz); + if (!prz->old_log) { persistent_ram_ecc_old(prz); prz->old_log = kvzalloc(size, GFP_KERNEL); -- 2.34.1