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
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
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: John Sobecki <john.sobecki@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Andreas Dilger <aedilger@xxxxxxxxx>
Cc: Alan Cox <alan@xxxxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnn@xxxxxxxx>
Cc: James Morris <james.l.morris@xxxxxxxxxx>
Cc: Ted Ts'o <tytso@xxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Jakub Jelinek <jakub@xxxxxxxxxx>
Cc: Ulrich Drepper <drepper@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/binfmt_elf.c | 26 +++++++++++++++++++++++++-
1 file changed, 25 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
@@ -48,6 +48,7 @@ static int load_elf_binary(struct linux_
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 *b
/*
* 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 +559,29 @@ static unsigned long randomize_stack_top
#endif
}
+/*
+ * A wrapper of get_random_int() to generate random bytes which has lower
+ * overhead than call 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() & STACK_RND_MASK;
+ random_variable <<= PAGE_SHIFT;
+
+ memcpy(p, &random_variable, chunk);
+ p += chunk;
+ nbytes -= chunk;
+ }
+}
+
static int load_elf_binary(struct linux_binprm *bprm)
{
struct file *interpreter = NULL; /* to shut gcc up */
_
Patches currently in -mm which might be from jeff.liu@xxxxxxxxxx are
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
binfmt_elfc-use-get_random_int-to-fix-entropy-depleting-fix.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
