[PATCH 05/10] mtd: afs: simplify partition parsing
Brian Norris
computersforpeace at gmail.com
Tue Nov 10 18:28:09 PST 2015
Hi Linus,
On Thu, Oct 15, 2015 at 03:08:48PM +0200, Linus Walleij wrote:
> This simplifies the AFS partition parsing to make the code
> more straight-forward and readable.
>
> Before this patch the code tried to calculate the memory required
> to hold the partition info by adding up the sizes of the strings
> of the names and adding that to a single memory allocation,
> indexing the name pointers in front of the struct mtd_partition
> allocations so all allocated data was in one chunk.
>
> This is overzealous. Instead use kstrdup and bail out,
> kfree():ing the memory used for MTD partitions and names alike
> on the errorpath.
>
> In the process rename the index variable from idx to i.
>
> Cc: Ryan Harkin <ryan.harkin at linaro.org>
> Cc: Liviu Dudau <liviu.dudau at arm.com>
> Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
> ---
> drivers/mtd/afs.c | 67 ++++++++++++++++++++++++++-----------------------------
> 1 file changed, 32 insertions(+), 35 deletions(-)
>
> diff --git a/drivers/mtd/afs.c b/drivers/mtd/afs.c
> index a1eea50ce180..9e6089615f16 100644
> --- a/drivers/mtd/afs.c
> +++ b/drivers/mtd/afs.c
> @@ -166,9 +166,9 @@ static int parse_afs_partitions(struct mtd_info *mtd,
> struct mtd_part_parser_data *data)
> {
> struct mtd_partition *parts;
> - u_int mask, off, idx, sz;
> + u_int mask, off, sz;
> int ret = 0;
> - char *str;
> + int i;
>
> /*
> * This is the address mask; we use this to mask off out of
> @@ -181,78 +181,75 @@ static int parse_afs_partitions(struct mtd_info *mtd,
> * partition information. We include in this the size of
> * the strings.
> */
Nit: you rewrite this comment in the next patch, when it really should
be rewritten here, since this is where you change the allocation
behavior. I wouldn't worry about this, except that I have other comments
below that I think you'll need to address.
> - for (idx = off = sz = 0; off < mtd->size; off += mtd->erasesize) {
> - struct image_info_v1 iis;
> + for (i = off = sz = 0; off < mtd->size; off += mtd->erasesize) {
> u_int iis_ptr, img_ptr;
>
> ret = afs_read_footer_v1(mtd, &img_ptr, &iis_ptr, off, mask);
> if (ret < 0)
> - break;
> + return ret;
> if (ret) {
> - ret = afs_read_iis_v1(mtd, &iis, iis_ptr);
> - if (ret < 0)
> - break;
> - if (ret == 0)
> - continue;
> -
> sz += sizeof(struct mtd_partition);
> - sz += strlen(iis.name) + 1;
> - idx += 1;
> + i += 1;
> }
> }
>
> - if (!sz)
> - return ret;
> + if (!i)
> + return 0;
>
> parts = kzalloc(sz, GFP_KERNEL);
> if (!parts)
> return -ENOMEM;
>
> - str = (char *)(parts + idx);
> -
> /*
> * Identify the partitions
> */
> - for (idx = off = 0; off < mtd->size; off += mtd->erasesize) {
> + for (i = off = 0; off < mtd->size; off += mtd->erasesize) {
> struct image_info_v1 iis;
> u_int iis_ptr, img_ptr;
>
> /* Read the footer. */
> ret = afs_read_footer_v1(mtd, &img_ptr, &iis_ptr, off, mask);
> if (ret < 0)
> - break;
> + goto out_free_parts;
> if (ret == 0)
> continue;
>
> /* Read the image info block */
> ret = afs_read_iis_v1(mtd, &iis, iis_ptr);
> if (ret < 0)
> - break;
> + goto out_free_parts;
> if (ret == 0)
> continue;
>
> - strcpy(str, iis.name);
> + parts[i].name = kstrdup(iis.name, GFP_KERNEL);
Unfortunately, there's a (sort of) good reason the name strings were
allocated along with the partition info all in one go; the calling code
expects to be able to kfree() just the struct to free up all the
parser's memory (see mtd_device_parse_register(), which does
kfree(real_parts)). So you're introducing N string allocations that will
never be freed in the "success" case -- i.e., a memory leak.
Now, it kinda sucks that MTD has such limited cleanup facilities for its
parsers. I believe we either have similar ugly code (or just more memory
leaks) in other parsers. It'd be nice if we added a cleanup hook to
struct mtd_part_parser, so we can allow parsers to do arbitrary
cleanups.
Brian
> + if (!parts[i].name) {
> + ret = -ENOMEM;
> + goto out_free_parts;
> + }
>
> - parts[idx].name = str;
> - parts[idx].size = (iis.length + mtd->erasesize - 1) & ~(mtd->erasesize - 1);
> - parts[idx].offset = img_ptr;
> - parts[idx].mask_flags = 0;
> + parts[i].size = (iis.length + mtd->erasesize - 1) & ~(mtd->erasesize - 1);
> + parts[i].offset = img_ptr;
> + parts[i].mask_flags = 0;
>
> printk(" mtd%d: at 0x%08x, %5lluKiB, %8u, %s\n",
> - idx, img_ptr, parts[idx].size / 1024,
> - iis.imageNumber, str);
> -
> - idx += 1;
> - str = str + strlen(iis.name) + 1;
> - }
> + i, img_ptr, parts[i].size / 1024,
> + iis.imageNumber, parts[i].name);
>
> - if (!idx) {
> - kfree(parts);
> - parts = NULL;
> + i += 1;
> }
>
> *pparts = parts;
> - return idx ? idx : ret;
> + return i;
> +
> +out_free_parts:
> + while (i >= 0) {
> + if (parts[i].name)
> + kfree(parts[i].name);
> + i--;
> + }
> + kfree(parts);
> + *pparts = NULL;
> + return ret;
> }
>
> static struct mtd_part_parser afs_parser = {
> --
> 2.4.3
>
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