[PATCH v6 2/7] treewide: use prandom_u32_max() when possible, part 2
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: 2022-10-10 23:08:35
Also in:
dri-devel, kernel-janitors, linux-block, linux-crypto, linux-doc, linux-fsdevel, linux-media, linux-mips, linux-mm, linux-mmc, linux-nvme, linux-patches, linux-rdma, linux-s390, linux-um, linux-usb, linux-wireless, linuxppc-dev, lkml, loongarch, sparclinux
Subsystem:
block layer, ext2 file system, ext4 file system, filesystems (vfs and infrastructure), library code, the rest, vmalloc · Maintainers:
Jens Axboe, Jan Kara, "Theodore Ts'o", Alexander Viro, Christian Brauner, Andrew Morton, Linus Torvalds, Uladzislau Rezki
Rather than incurring a division or requesting too many random bytes for the given range, use the prandom_u32_max() function, which only takes the minimum required bytes from the RNG and avoids divisions. This was done by hand, covering things that coccinelle could not do on its own. Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Reviewed-by: Kees Cook <redacted> Reviewed-by: Yury Norov <yury.norov@gmail.com> Reviewed-by: Jan Kara <jack@suse.cz> # for ext2, ext4, and sbitmap Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> --- fs/ext2/ialloc.c | 3 +-- fs/ext4/ialloc.c | 5 ++--- lib/sbitmap.c | 2 +- lib/test_vmalloc.c | 17 ++++------------- 4 files changed, 8 insertions(+), 19 deletions(-)
diff --git a/fs/ext2/ialloc.c b/fs/ext2/ialloc.c
index 998dd2ac8008..f4944c4dee60 100644
--- a/fs/ext2/ialloc.c
+++ b/fs/ext2/ialloc.c@@ -277,8 +277,7 @@ static int find_group_orlov(struct super_block *sb, struct inode *parent) int best_ndir = inodes_per_group; int best_group = -1; - group = prandom_u32(); - parent_group = (unsigned)group % ngroups; + parent_group = prandom_u32_max(ngroups); for (i = 0; i < ngroups; i++) { group = (parent_group + i) % ngroups; desc = ext2_get_group_desc (sb, group, NULL);
diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 208b87ce8858..7575aa359675 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c@@ -463,10 +463,9 @@ static int find_group_orlov(struct super_block *sb, struct inode *parent, hinfo.hash_version = DX_HASH_HALF_MD4; hinfo.seed = sbi->s_hash_seed; ext4fs_dirhash(parent, qstr->name, qstr->len, &hinfo); - grp = hinfo.hash; + parent_group = hinfo.hash % ngroups; } else - grp = prandom_u32(); - parent_group = (unsigned)grp % ngroups; + parent_group = prandom_u32_max(ngroups); for (i = 0; i < ngroups; i++) { g = (parent_group + i) % ngroups; get_orlov_stats(sb, g, flex_size, &stats);
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 055dac069afb..7280ae8ca88c 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c@@ -21,7 +21,7 @@ static int init_alloc_hint(struct sbitmap *sb, gfp_t flags) int i; for_each_possible_cpu(i) - *per_cpu_ptr(sb->alloc_hint, i) = prandom_u32() % depth; + *per_cpu_ptr(sb->alloc_hint, i) = prandom_u32_max(depth); } return 0; }
diff --git a/lib/test_vmalloc.c b/lib/test_vmalloc.c
index 4f2f2d1bac56..a26bbbf20e62 100644
--- a/lib/test_vmalloc.c
+++ b/lib/test_vmalloc.c@@ -151,9 +151,7 @@ static int random_size_alloc_test(void) int i; for (i = 0; i < test_loop_count; i++) { - n = prandom_u32(); - n = (n % 100) + 1; - + n = prandom_u32_max(100) + 1; p = vmalloc(n * PAGE_SIZE); if (!p)
@@ -293,16 +291,12 @@ pcpu_alloc_test(void) return -1; for (i = 0; i < 35000; i++) { - unsigned int r; - - r = prandom_u32(); - size = (r % (PAGE_SIZE / 4)) + 1; + size = prandom_u32_max(PAGE_SIZE / 4) + 1; /* * Maximum PAGE_SIZE */ - r = prandom_u32(); - align = 1 << ((r % 11) + 1); + align = 1 << (prandom_u32_max(11) + 1); pcpu[i] = __alloc_percpu(size, align); if (!pcpu[i])
@@ -393,14 +387,11 @@ static struct test_driver { static void shuffle_array(int *arr, int n) { - unsigned int rnd; int i, j; for (i = n - 1; i > 0; i--) { - rnd = prandom_u32(); - /* Cut the range. */ - j = rnd % i; + j = prandom_u32_max(i); /* Swap indexes. */ swap(arr[i], arr[j]);
--
2.37.3