The patch titled
Subject: binfmt_elf.c: use get_random_int() to fix entropy depleting
has been added to the -mm tree. Its filename is
binfmt_elfc-use-get_random_int-to-fix-entropy-depleting.patch
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------------------------------------------------------
From: Jeff Liu <jeff.liu@xxxxxxxxxx>
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.
Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Andreas Dilger <aedilger@xxxxxxxxx>
Cc: Alan Cox <alan@xxxxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnn@xxxxxxxx>
Cc: John Sobecki <john.sobecki@xxxxxxxxxx>
Cc: James Morris <james.l.morris@xxxxxxxxxx>
Cc: Jakub Jelinek <jakub@xxxxxxxxxx>
Cc: Ted Ts'o <tytso@xxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Ulrich Drepper <drepper@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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
@@ -139,6 +139,25 @@ 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)
@@ -200,7 +219,7 @@ 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)))
_
Patches currently in -mm which might be from jeff.liu@xxxxxxxxxx are
linux-next.patch
documentation-cgroups-memorytxt-s-mem_cgroup_charge-mem_cgroup_change_common.patch
mm-vmscanc-try_to_freeze-returns-boolean.patch
binfmt_elfc-use-get_random_int-to-fix-entropy-depleting.patch
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