Messages in this thread Patch in this message | | | Date | Wed, 07 Nov 2012 13:27:15 +0800 | From | Jeff Liu <> | Subject | [PATCH V3] binfmt_elf.c: Introduce a wrapper of get_random_int() to fix entropy depleting |
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Hello,
We have observed entropy quickly depleting under normal I/O between 2.6.30 to upstream, 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
It has been occurred with fs/binfmt_elf.c: create_elf_tables()->get_random_bytes() was introduced began at 2.6.30. /* * Generate 16 random bytes for userspace PRNG seeding. */ get_random_bytes(k_rand_bytes, sizeof(k_rand_bytes));
This proposal patch is trying to introduce a wrapper of get_random_int() which has lower overhead than calling get_random_bytes() directly.
Entropy increased 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
v3->v2: ------- Remove redundant bits mask and shift upon the random variable according to Kees's review.
v2->v1: ------- Fix random copy to check up buffer length that are not 4-byte multiples according to Andreas's comments.
v2 can be found at: http://www.spinics.net/lists/linux-fsdevel/msg59418.html v1 can be found at: http://www.spinics.net/lists/linux-fsdevel/msg59128.html
Many thanks to Andreas, Andrew as well as Kees for reviewing the patch of past.
-Jeff
Signed-off-by: Jie Liu <jeff.liu@oracle.com> Cc: John Sobecki <john.sobecki@oracle.com> CC: Andrew Morton <akpm@linux-foundation.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Andreas Dilger <aedilger@gmail.com> Cc: Alan Cox <alan@linux.intel.com> Cc: Arnd Bergmann <arnn@arndb.de> Cc: James Morris <james.l.morris@oracle.com> Cc: Ted Ts'o <tytso@mit.edu> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Kees Cook <keescook@chromium.org> Cc: Jakub Jelinek <jakub@redhat.com> Cc: Ulrich Drepper <drepper@redhat.com>
--- fs/binfmt_elf.c | 24 +++++++++++++++++++++++- 1 files changed, 23 insertions(+), 1 deletions(-)
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index fbd9f60..9c36e50 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -48,6 +48,7 @@ static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs); static int load_elf_library(struct file *); static unsigned long elf_map(struct file *, unsigned long, struct elf_phdr *, int, int, unsigned long); +static void randomize_stack_user(unsigned char *buf, size_t nbytes); /* * If we don't support core dumping, then supply a NULL so we @@ -200,7 +201,7 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec, /* * Generate 16 random bytes for userspace PRNG seeding. */ - get_random_bytes(k_rand_bytes, sizeof(k_rand_bytes)); + randomize_stack_user(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))) @@ -558,6 +559,27 @@ static unsigned long randomize_stack_top(unsigned long stack_top) #endif } +/* + * A wrapper of get_random_int() to generate random bytes which has lower + * overhead than calling get_random_bytes() directly. + * create_elf_tables() call this function to generate 16 random bytes for + * userspace PRNG seeding. + */ +static void randomize_stack_user(unsigned char *buf, size_t nbytes) +{ + unsigned char *p = buf; + + while (nbytes) { + unsigned int random_variable; + size_t chunk = min(nbytes, sizeof(unsigned int)); + + random_variable = get_random_int(); + memcpy(p, &random_variable, chunk); + p += chunk; + nbytes -= chunk; + } +} + static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs) { struct file *interpreter = NULL; /* to shut gcc up */ -- 1.7.4.1
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