From: Sai Ritvik Tanksalkar <[email protected]>
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 ...
Fix this by freeing and reallocating the buffer when the new size
exceeds 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")
Cc: [email protected]
Signed-off-by: Sai Ritvik Tanksalkar <[email protected]>
---
v2: Fixed Signed-off-by to use real name (was using Github ID).
Resending with proper mail client to preserve tabs.
fs/pstore/ram_core.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
index f1848cdd6d34..8df813a42a41 100644
--- a/fs/pstore/ram_core.c
+++ b/fs/pstore/ram_core.c
@@ -298,6 +298,14 @@ void persistent_ram_save_old(struct persistent_ram_zone
*prz)
if (!size)
return;
+ /*
+ * If the existing buffer is too small, free it so a new one is
+ * allocated. This can happen when persistent_ram_save_old() is
+ * called multiple times with different 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);
--
2.43.0
