Quoting David Daney :
On 08/16/2012 02:20 PM, Kasatkin, Dmitry wrote:
Hello,
Some places in the code uses variable-size allocation on stack..
For example from hmac_setkey():
struct {
struct shash_desc shash;
char ctx[crypto_shash_descsize(hash)];
} desc;
sparse complains
CHECK crypto/hmac.c
crypto/hmac.c:57:47: error: bad constant expression
I like it instead of kmalloc..
But what is position of kernel community about it?
If you know that the range of crypto_shash_descsize(hash) is
bounded, just use the upper bound.
If the range of crypto_shash_descsize(hash) is unbounded, then the
stack will overflow and ... BOOM!
Quick look shows that largest crypto_shash_descsize() would be with
hmac+s390/sha512, 16 + 332 = 348. Crypto-api also prevents registering
shash with descsize larger than (PAGE_SIZE / 8).
-Jussi
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