[PATCH v3 1/3] nvmem: core: improve range check for nvmem_cell_write()

Jennifer Berringer
2024-11-04T15:24:26Z

When __nvmem_cell_entry_write() is called for an nvmem cell that does
not need bit shifting, it requires that the len parameter exactly
matches the nvmem cell size. However, when the nvmem cell has a nonzero
bit_offset, it was skipping this check.

Accepting values of len larger than the cell size results in
nvmem_cell_prepare_write_buffer() trying to write past the end of a heap
buffer that it allocates. Add a check to avoid that problem and instead
return -EINVAL when len doesn't match the number of bits expected by the
nvmem cell when bit_offset is nonzero.

This check uses cell->nbits in order to allow providing the smaller size
to cells that are shifted into another byte by bit_offset. For example,
a cell with nbits=8 and nonzero bit_offset would have bytes=2 but should
accept a 1-byte write here, although no current callers depend on this.

Fixes: 69aba7948cbe ("nvmem: Add a simple NVMEM framework for consumers")

Signed-off-by: Jennifer Berringer <jberring@redhat.com>
---
drivers/nvmem/core.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index 33ffa2aa4c11..4a5a6efe4bab 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -1780,6 +1780,8 @@ static int __nvmem_cell_entry_write(struct nvmem_cell_entry *cell, void *buf, si
return -EINVAL;

if (cell->bit_offset || cell->nbits) {
+ if (len != BITS_TO_BYTES(cell->nbits) && len != cell->bytes)
+ return -EINVAL;
buf = nvmem_cell_prepare_write_buffer(cell, buf, len);
if (IS_ERR(buf))
return PTR_ERR(buf);
--
2.46.2