[PATCH 2/2] pstore: reject persistent RAM zones too small for the buffer header

[Andrea Parri <parri.andrea@gmail.com>]

persistent_ram_buffer_map() computes

	prz->buffer_size = size - sizeof(struct persistent_ram_buffer);

without checking that size is large enough to hold the header.  A
ramoops zone configured with a tiny size (e.g. ramoops.pmsg_size=1)
underflows buffer_size to a huge value, which defeats every bounds
check in persistent_ram_write() and persistent_ram_write_user(); a
write to /dev/pmsg0 then copies user data far past the end of the zone
and corrupts kernel memory.

Reject zones that are not larger than the buffer header.

Fixes: 404a6043385de ("staging: android: persistent_ram: handle reserving and mapping memory")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
---
 fs/pstore/ram_core.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
index b4ec8009b8dc9..ae941777037b8 100644
--- a/fs/pstore/ram_core.c
+++ b/fs/pstore/ram_core.c
@@ -505,6 +505,12 @@ static int persistent_ram_buffer_map(phys_addr_t start, phys_addr_t size,
 	prz->paddr = start;
 	prz->size = size;
 
+	if (size <= sizeof(struct persistent_ram_buffer)) {
+		pr_err("%s: persistent ram zone too small (%#llx bytes)\n",
+		       prz->label, (unsigned long long)size);
+		return -EINVAL;
+	}
+
 	if (pfn_valid(start >> PAGE_SHIFT))
 		prz->vaddr = persistent_ram_vmap(start, size, memtype);
 	else
-- 
2.53.0