[PATCH -next] pstore/ram: Do not use stack VLA for parity workspace

[Kees Cook]

Instead of using a stack VLA for the parity workspace, preallocate a
memory region. The preallocation is done to keep from needing to perform
allocations during crash dump writing, etc. This also fixes a missed
release of librs on free.

Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 fs/pstore/ram_core.c       | 29 ++++++++++++++++++++++-------
 include/linux/pstore_ram.h |  1 +
 2 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
index e11672aa4575..951a14edcf51 100644
--- a/fs/pstore/ram_core.c
+++ b/fs/pstore/ram_core.c
@@ -98,24 +98,23 @@ static void notrace persistent_ram_encode_rs8(struct 
persistent_ram_zone *prz,
        uint8_t *data, size_t len, uint8_t *ecc)
 {
        int i;
-       uint16_t par[prz->ecc_info.ecc_size];
 
        /* Initialize the parity buffer */
-       memset(par, 0, sizeof(par));
-       encode_rs8(prz->rs_decoder, data, len, par, 0);
+       memset(prz->ecc_info.par, 0,
+              prz->ecc_info.ecc_size * sizeof(prz->ecc_info.par[0]));
+       encode_rs8(prz->rs_decoder, data, len, prz->ecc_info.par, 0);
        for (i = 0; i < prz->ecc_info.ecc_size; i++)
-               ecc[i] = par[i];
+               ecc[i] = prz->ecc_info.par[i];
 }
 
 static int persistent_ram_decode_rs8(struct persistent_ram_zone *prz,
        void *data, size_t len, uint8_t *ecc)
 {
        int i;
-       uint16_t par[prz->ecc_info.ecc_size];
 
        for (i = 0; i < prz->ecc_info.ecc_size; i++)
-               par[i] = ecc[i];
-       return decode_rs8(prz->rs_decoder, data, par, len,
+               prz->ecc_info.par[i] = ecc[i];
+       return decode_rs8(prz->rs_decoder, data, prz->ecc_info.par, len,
                                NULL, 0, NULL, 0, NULL);
 }
 
@@ -228,6 +227,15 @@ static int persistent_ram_init_ecc(struct 
persistent_ram_zone *prz,
                return -EINVAL;
        }
 
+       /* allocate workspace instead of using stack VLA */
+       prz->ecc_info.par = kmalloc_array(prz->ecc_info.ecc_size,
+                                         sizeof(*prz->ecc_info.par),
+                                         GFP_KERNEL);
+       if (!prz->ecc_info.par) {
+               pr_err("cannot allocate ECC parity workspace\n");
+               return -ENOMEM;
+       }
+
        prz->corrected_bytes = 0;
        prz->bad_blocks = 0;
 
@@ -514,6 +522,13 @@ void persistent_ram_free(struct persistent_ram_zone *prz)
                }
                prz->vaddr = NULL;
        }
+       if (prz->rs_decoder) {
+               free_rs(prz->rs_decoder);
+               prz->rs_decoder = NULL;
+       }
+       kfree(prz->ecc_info.par);
+       prz->ecc_info.par = NULL;
+
        persistent_ram_free_old(prz);
        kfree(prz);
 }
diff --git a/include/linux/pstore_ram.h b/include/linux/pstore_ram.h
index 9395f06e8372..e6d226464838 100644
--- a/include/linux/pstore_ram.h
+++ b/include/linux/pstore_ram.h
@@ -39,6 +39,7 @@ struct persistent_ram_ecc_info {
        int ecc_size;
        int symsize;
        int poly;
+       uint16_t *par;
 };
 
 struct persistent_ram_zone {
-- 
2.7.4


-- 
Kees Cook
Pixel Security