pstore/ram: Do not use stack VLA for parity workspace

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 <keescook@chromium.org>

1 files changed, 22 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);
 }