Commit b5f51573 authored by Andreas Dilger's avatar Andreas Dilger Committed by Theodore Ts'o

ext4: avoid Y2038 overflow in recently_deleted()

Avoid a 32-bit time overflow in recently_deleted() since i_dtime
(inode deletion time) is stored only as a 32-bit value on disk.
Since i_dtime isn't used for much beyond a boolean value in e2fsck
and is otherwise only used in this function in the kernel, there is
no benefit to use more space in the inode for this field on disk.

Instead, compare only the relative deletion time with the low
32 bits of the time using the newly-added time_before32() helper,
which is similar to time_before() and time_after() for jiffies.

Increase RECENTCY_DIRTY to 300s based on Ted's comments about
usage experience at Google.
Signed-off-by: default avatarAndreas Dilger <adilger@dilger.ca>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Reviewed-by: default avatarArnd Bergmann <arnd@arndb.de>
parent fd96b8da
...@@ -692,16 +692,17 @@ static int find_group_other(struct super_block *sb, struct inode *parent, ...@@ -692,16 +692,17 @@ static int find_group_other(struct super_block *sb, struct inode *parent,
* somewhat arbitrary...) * somewhat arbitrary...)
*/ */
#define RECENTCY_MIN 5 #define RECENTCY_MIN 5
#define RECENTCY_DIRTY 30 #define RECENTCY_DIRTY 300
static int recently_deleted(struct super_block *sb, ext4_group_t group, int ino) static int recently_deleted(struct super_block *sb, ext4_group_t group, int ino)
{ {
struct ext4_group_desc *gdp; struct ext4_group_desc *gdp;
struct ext4_inode *raw_inode; struct ext4_inode *raw_inode;
struct buffer_head *bh; struct buffer_head *bh;
unsigned long dtime, now;
int inodes_per_block = EXT4_SB(sb)->s_inodes_per_block; int inodes_per_block = EXT4_SB(sb)->s_inodes_per_block;
int offset, ret = 0, recentcy = RECENTCY_MIN; int offset, ret = 0;
int recentcy = RECENTCY_MIN;
u32 dtime, now;
gdp = ext4_get_group_desc(sb, group, NULL); gdp = ext4_get_group_desc(sb, group, NULL);
if (unlikely(!gdp)) if (unlikely(!gdp))
...@@ -718,12 +719,18 @@ static int recently_deleted(struct super_block *sb, ext4_group_t group, int ino) ...@@ -718,12 +719,18 @@ static int recently_deleted(struct super_block *sb, ext4_group_t group, int ino)
offset = (ino % inodes_per_block) * EXT4_INODE_SIZE(sb); offset = (ino % inodes_per_block) * EXT4_INODE_SIZE(sb);
raw_inode = (struct ext4_inode *) (bh->b_data + offset); raw_inode = (struct ext4_inode *) (bh->b_data + offset);
/* i_dtime is only 32 bits on disk, but we only care about relative
* times in the range of a few minutes (i.e. long enough to sync a
* recently-deleted inode to disk), so using the low 32 bits of the
* clock (a 68 year range) is enough, see time_before32() */
dtime = le32_to_cpu(raw_inode->i_dtime); dtime = le32_to_cpu(raw_inode->i_dtime);
now = get_seconds(); now = ktime_get_real_seconds();
if (buffer_dirty(bh)) if (buffer_dirty(bh))
recentcy += RECENTCY_DIRTY; recentcy += RECENTCY_DIRTY;
if (dtime && (dtime < now) && (now < dtime + recentcy)) if (dtime && time_before32(dtime, now) &&
time_before32(now, dtime + recentcy))
ret = 1; ret = 1;
out: out:
brelse(bh); brelse(bh);
......
...@@ -285,4 +285,19 @@ static inline bool itimerspec64_valid(const struct itimerspec64 *its) ...@@ -285,4 +285,19 @@ static inline bool itimerspec64_valid(const struct itimerspec64 *its)
return true; return true;
} }
/**
* time_after32 - compare two 32-bit relative times
* @a: the time which may be after @b
* @b: the time which may be before @a
*
* time_after32(a, b) returns true if the time @a is after time @b.
* time_before32(b, a) returns true if the time @b is before time @a.
*
* Similar to time_after(), compare two 32-bit timestamps for relative
* times. This is useful for comparing 32-bit seconds values that can't
* be converted to 64-bit values (e.g. due to disk format or wire protocol
* issues) when it is known that the times are less than 68 years apart.
*/
#define time_after32(a, b) ((s32)((u32)(b) - (u32)(a)) < 0)
#define time_before32(b, a) time_after32(a, b)
#endif #endif
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment