Messages in this thread | | | Date | Fri, 2 Nov 2018 11:24:54 -0700 | From | Joel Fernandes <> | Subject | Re: [PATCH 2/8] pstore: Do not use crash buffer for decompression |
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On Thu, Nov 01, 2018 at 04:51:54PM -0700, Kees Cook wrote: > The pre-allocated compression buffer used for crash dumping was also > being used for decompression. This isn't technically safe, since it's > possible the kernel may attempt a crashdump while pstore is populating the > pstore filesystem (and performing decompression). Instead, just allocate
Yeah, that would be bad if it happened ;)
> a separate buffer for decompression. Correctness is preferred over > performance here. > > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > fs/pstore/platform.c | 56 ++++++++++++++++++++------------------------ > 1 file changed, 25 insertions(+), 31 deletions(-) > > diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c > index b821054ca3ed..8b6028948cf3 100644 > --- a/fs/pstore/platform.c > +++ b/fs/pstore/platform.c > @@ -258,20 +258,6 @@ static int pstore_compress(const void *in, void *out, > return outlen; > } > > -static int pstore_decompress(void *in, void *out, > - unsigned int inlen, unsigned int outlen) > -{ > - int ret; > - > - ret = crypto_comp_decompress(tfm, in, inlen, out, &outlen); > - if (ret) { > - pr_err("crypto_comp_decompress failed, ret = %d!\n", ret); > - return ret; > - } > - > - return outlen; > -} > - > static void allocate_buf_for_compression(void) > { > struct crypto_comp *ctx; > @@ -656,8 +642,9 @@ EXPORT_SYMBOL_GPL(pstore_unregister); > > static void decompress_record(struct pstore_record *record) > { > + int ret; > int unzipped_len;
nit: We could get rid of the unzipped_len variable now I think.
> - char *decompressed; > + char *unzipped, *workspace; > > if (!record->compressed) > return; > @@ -668,35 +655,42 @@ static void decompress_record(struct pstore_record *record) > return; > } > > - /* No compression method has created the common buffer. */ > + /* Missing compression buffer means compression was not initialized. */ > if (!big_oops_buf) { > - pr_warn("no decompression buffer allocated\n"); > + pr_warn("no decompression method initialized!\n"); > return; > } > > - unzipped_len = pstore_decompress(record->buf, big_oops_buf, > - record->size, big_oops_buf_sz); > - if (unzipped_len <= 0) { > - pr_err("decompression failed: %d\n", unzipped_len); > + /* Allocate enough space to hold max decompression and ECC. */ > + unzipped_len = big_oops_buf_sz; > + workspace = kmalloc(unzipped_len + record->ecc_notice_size,
Should tihs be unzipped_len + record->ecc_notice_size + 1. The extra byte being for the NULL character of the ecc notice?
This occurred to me when I saw the + 1 in ram.c. It could be better to just abstract the size as a macro.
> + GFP_KERNEL); > + if (!workspace) > return; > - } > > - /* Build new buffer for decompressed contents. */ > - decompressed = kmalloc(unzipped_len + record->ecc_notice_size, > - GFP_KERNEL); > - if (!decompressed) { > - pr_err("decompression ran out of memory\n"); > + /* After decompression "unzipped_len" is almost certainly smaller. */ > + ret = crypto_comp_decompress(tfm, record->buf, record->size, > + workspace, &unzipped_len); > + if (ret) { > + pr_err("crypto_comp_decompress failed, ret = %d!\n", ret); > + kfree(workspace); > return; > } > - memcpy(decompressed, big_oops_buf, unzipped_len); > > /* Append ECC notice to decompressed buffer. */ > - memcpy(decompressed + unzipped_len, record->buf + record->size, > + memcpy(workspace + unzipped_len, record->buf + record->size, > record->ecc_notice_size); > > - /* Swap out compresed contents with decompressed contents. */ > + /* Copy decompressed contents into an minimum-sized allocation. */ > + unzipped = kmemdup(workspace, unzipped_len + record->ecc_notice_size, > + GFP_KERNEL); > + kfree(workspace); > + if (!unzipped) > + return; > + > + /* Swap out compressed contents with decompressed contents. */ > kfree(record->buf); > - record->buf = decompressed; > + record->buf = unzipped;
Rest of it LGTM, thanks!
- Joel
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