[PATCH 5.10 300/406] pstore/ram: Check start of empty przs during init

Greg Kroah-Hartman
2023-09-17T19:37:32Z

From: Enlin Mu <enlin.mu@unisoc.com>

commit fe8c3623ab06603eb760444a032d426542212021 upstream.

After commit 30696378f68a ("pstore/ram: Do not treat empty buffers as
valid"), initialization would assume a prz was valid after seeing that
the buffer_size is zero (regardless of the buffer start position). This
unchecked start value means it could be outside the bounds of the buffer,
leading to future access panics when written to:

sysdump_panic_event+0x3b4/0x5b8
atomic_notifier_call_chain+0x54/0x90
panic+0x1c8/0x42c
die+0x29c/0x2a8
die_kernel_fault+0x68/0x78
__do_kernel_fault+0x1c4/0x1e0
do_bad_area+0x40/0x100
do_translation_fault+0x68/0x80
do_mem_abort+0x68/0xf8
el1_da+0x1c/0xc0
__raw_writeb+0x38/0x174
__memcpy_toio+0x40/0xac
persistent_ram_update+0x44/0x12c
persistent_ram_write+0x1a8/0x1b8
ramoops_pstore_write+0x198/0x1e8
pstore_console_write+0x94/0xe0
...

To avoid this, also check if the prz start is 0 during the initialization
phase. If not, the next prz sanity check case will discover it (start >
size) and zap the buffer back to a sane state.

Fixes: 30696378f68a ("pstore/ram: Do not treat empty buffers as valid")
Cc: Yunlong Xing <yunlong.xing@unisoc.com>
Cc: stable@vger.kernel.org
Signed-off-by: Enlin Mu <enlin.mu@unisoc.com>
Link: https://lore.kernel.org/r/20230801060432.1307717-1-yunlong.xing@unisoc.com
[kees: update commit log with backtrace and clarifications]
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/pstore/ram_core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/pstore/ram_core.c
+++ b/fs/pstore/ram_core.c
@@ -504,7 +504,7 @@ static int persistent_ram_post_init(stru
sig ^= PERSISTENT_RAM_SIG;

if (prz->buffer->sig == sig) {
- if (buffer_size(prz) == 0) {
+ if (buffer_size(prz) == 0 && buffer_start(prz) == 0) {
pr_debug("found existing empty buffer\n");
return 0;
}