nvmem: core: improve range check for nvmem_cell_write()

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")
Cc: stable@vger.kernel.org
Signed-off-by: Jennifer Berringer <jberring@redhat.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20241230141901.263976-7-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index fd09f1a6917fe8a43cc7b112d3611b1e000c7c16..fff85bbf0ecd0f638e21f127370105d9f79c00d2 100644 (file)
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -1793,6 +1793,8 @@ 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);