4.14-stable review patch. If anyone has any objections, please let me know.
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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 @@ -492,7 +492,7 @@ 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; }