On Thu, 07 Nov 2013 12:14:17 +0800 Jeff Liu <jeff....@oracle.com> wrote:
> Hi Stephan, > > As per your previous comments for this fix, you have promised another > approach which > is promising to avoid entropy starvation, I got this info from the following > thread: > [PATCH] avoid entropy starvation due to stack protection > https://lkml.org/lkml/2012/12/14/267 > > My current fix has been merged into Andrew's tree(marked in "stuck" state) > for a long > time, and it also works well in our internal specific kernel, I'd like to > know if there > is any update from you, so that we can move it along for mainline. :) This: From: Jeff Liu <jeff....@oracle.com> Subject: binfmt_elf.c: use get_random_int() to fix entropy depleting Entropy is quickly depleted under normal operations like ls(1), cat(1), etc... between 2.6.30 to current mainline, for instance: $ cat /proc/sys/kernel/random/entropy_avail 3428 $ cat /proc/sys/kernel/random/entropy_avail 2911 $cat /proc/sys/kernel/random/entropy_avail 2620 We observed this problem has been occurring since 2.6.30 with fs/binfmt_elf.c: create_elf_tables()->get_random_bytes(), introduced by f06295b44c296c8f ("ELF: implement AT_RANDOM for glibc PRNG seeding"). /* * Generate 16 random bytes for userspace PRNG seeding. */ get_random_bytes(k_rand_bytes, sizeof(k_rand_bytes)); The patch introduces a wrapper around get_random_int() which has lower overhead than calling get_random_bytes() directly. With this patch applied: $ cat /proc/sys/kernel/random/entropy_avail 2731 $ cat /proc/sys/kernel/random/entropy_avail 2802 $ cat /proc/sys/kernel/random/entropy_avail 2878 Analyzed by John Sobecki. This has been applied on a specific Oracle kernel and has been running on the customer's production environment (the original bug reporter) for several months; it has worked fine until now. Signed-off-by: Jie Liu <jeff....@oracle.com> Cc: Al Viro <v...@zeniv.linux.org.uk> Cc: Andreas Dilger <aedil...@gmail.com> Cc: Alan Cox <a...@linux.intel.com> Cc: Arnd Bergmann <a...@arndb.de> Cc: John Sobecki <john.sobe...@oracle.com> Cc: James Morris <james.l.mor...@oracle.com> Cc: Jakub Jelinek <ja...@redhat.com> Cc: Ted Ts'o <ty...@mit.edu> Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org> Acked-by: Kees Cook <keesc...@chromium.org> Cc: Ulrich Drepper <drep...@redhat.com> Signed-off-by: Andrew Morton <a...@linux-foundation.org> --- fs/binfmt_elf.c | 21 ++++++++++++++++++++- 1 file changed, 20 insertions(+), 1 deletion(-) diff -puN fs/binfmt_elf.c~binfmt_elfc-use-get_random_int-to-fix-entropy-depleting fs/binfmt_elf.c --- a/fs/binfmt_elf.c~binfmt_elfc-use-get_random_int-to-fix-entropy-depleting +++ a/fs/binfmt_elf.c @@ -140,6 +140,25 @@ static int padzero(unsigned long elf_bss #define ELF_BASE_PLATFORM NULL #endif +/* + * Use get_random_int() to implement AT_RANDOM while avoiding depletion + * of the entropy pool. + */ +static void get_atrandom_bytes(unsigned char *buf, size_t nbytes) +{ + unsigned char *p = buf; + + while (nbytes) { + unsigned int random_variable; + size_t chunk = min(nbytes, sizeof(random_variable)); + + random_variable = get_random_int(); + memcpy(p, &random_variable, chunk); + p += chunk; + nbytes -= chunk; + } +} + static int create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec, unsigned long load_addr, unsigned long interp_load_addr) @@ -201,7 +220,7 @@ create_elf_tables(struct linux_binprm *b /* * Generate 16 random bytes for userspace PRNG seeding. */ - get_random_bytes(k_rand_bytes, sizeof(k_rand_bytes)); + get_atrandom_bytes(k_rand_bytes, sizeof(k_rand_bytes)); u_rand_bytes = (elf_addr_t __user *) STACK_ALLOC(p, sizeof(k_rand_bytes)); if (__copy_to_user(u_rand_bytes, k_rand_bytes, sizeof(k_rand_bytes))) _ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
