sters, 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 Link: https://patch.msgid.link/20260201132240.2948732-1-stanksal@purdue.edu Signed-off-by: Kees Cook Signed-off-by: Sasha Levin --- 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 f1848cdd6d348..c9eaacdec37e4 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); -- 2.51.0[PATCH 6.18 126/641] pstore/ram: fix buffer overflow in persistent_ram_save_old()Greg Kroah-Hartman undefinedstable@vger.kernel.org undefined undefined undefined undefined undefinedŒA†“k