Allow read only mounts for filesystems that do not have maximum timestamps beyond the y2038 expiry timestamp.

Also, allow a sysctl override to all such filesystems to be mounted with write permissions. A boot param supports initial override of these checks from the early boot without recompilation.

Suggested-by: Arnd Bergmann arnd@arndb.de Signed-off-by: Deepa Dinamani deepa.kernel@gmail.com --- fs/inode.c | 15 +++++++++++++++ fs/internal.h | 2 ++ fs/namespace.c | 12 ++++++++++++ fs/super.c | 7 +++++++ include/linux/fs.h | 1 + include/linux/time64.h | 4 ++++ include/uapi/linux/fs.h | 6 +++++- kernel/sysctl.c | 7 +++++++ 8 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/fs/inode.c b/fs/inode.c index 0b3ee89..7967f9c 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -75,6 +75,21 @@ static DEFINE_PER_CPU(unsigned long, nr_unused);

static struct kmem_cache *inode_cachep __read_mostly;

+struct vfs_max_timestamp_check timestamp_check = { + .timestamp_supported = Y2038_EXPIRY_TIMESTAMP, + .check_on = 0, +}; + +static int __init setup_timestamp_check(char *str) +{ + if (*str) + return 0; + timestamp_check.check_on = 1; + return 1; +} + +__setup("fstimestampcheck", setup_timestamp_check); + static long get_nr_inodes(void) { int i; diff --git a/fs/internal.h b/fs/internal.h index 11c6d89..4b3cb9e 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -67,6 +67,8 @@ extern int finish_automount(struct vfsmount *, struct path *);

extern int sb_prepare_remount_readonly(struct super_block *);

+extern bool sb_file_times_updatable(struct super_block *sb); + extern void __init mnt_init(void);

extern int __mnt_want_write(struct vfsmount *); diff --git a/fs/namespace.c b/fs/namespace.c index 8bfad42..dbf3f1c 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -538,6 +538,18 @@ static void __mnt_unmake_readonly(struct mount *mnt) unlock_mount_hash(); }

+bool sb_file_times_updatable(struct super_block *sb) +{ + + if (!timestamp_check.check_on) + return true; + + if (sb->s_time_max > timestamp_check.timestamp_supported) + return true; + + return false; +} + int sb_prepare_remount_readonly(struct super_block *sb) { struct mount *mnt; diff --git a/fs/super.c b/fs/super.c index f9c2241..4e7577b 100644 --- a/fs/super.c +++ b/fs/super.c @@ -1245,6 +1245,13 @@ mount_fs(struct file_system_type *type, int flags, const char *name, void *data) WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to " "negative value (%lld)\n", type->name, sb->s_maxbytes);

+ if (!(sb->s_flags & MS_RDONLY) && !sb_file_times_updatable(sb)) { + WARN(1, "File times cannot be updated on the filesystem.\n"); + WARN(1, "Retry mounting the filesystem readonly.\n"); + error = -EROFS; + goto out_sb; + } + up_write(&sb->s_umount); free_secdata(secdata); return root; diff --git a/include/linux/fs.h b/include/linux/fs.h index ef55dfb..e12a32d 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -68,6 +68,7 @@ extern struct inodes_stat_t inodes_stat; extern int leases_enable, lease_break_time; extern int sysctl_protected_symlinks; extern int sysctl_protected_hardlinks; +extern struct vfs_max_timestamp_check timestamp_check;

struct buffer_head; typedef int (get_block_t)(struct inode *inode, sector_t iblock, diff --git a/include/linux/time64.h b/include/linux/time64.h index 25433b18..906e0b3 100644 --- a/include/linux/time64.h +++ b/include/linux/time64.h @@ -43,6 +43,10 @@ struct itimerspec64 { #define KTIME_MAX ((s64)~((u64)1 << 63)) #define KTIME_SEC_MAX (KTIME_MAX / NSEC_PER_SEC)

+/* Timestamps on boundary */ +#define Y2038_EXPIRY_TIMESTAMP S32_MAX /* 2147483647 */ +#define Y2106_EXPIRY_TIMESTAMP U32_MAX /* 4294967295 */ + #if __BITS_PER_LONG == 64

static inline struct timespec timespec64_to_timespec(const struct timespec64 ts64) diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h index 048a85e..125e4ae 100644 --- a/include/uapi/linux/fs.h +++ b/include/uapi/linux/fs.h @@ -91,6 +91,11 @@ struct files_stat_struct { unsigned long max_files; /* tunable */ };

+struct vfs_max_timestamp_check { + time64_t timestamp_supported; + int check_on; +}; + struct inodes_stat_t { long nr_inodes; long nr_unused; @@ -100,7 +105,6 @@ struct inodes_stat_t {

#define NR_FILE 8192 /* this can well be larger on a larger system */

- /* * These are the fs-independent mount-flags: up to 32 flags are supported */ diff --git a/kernel/sysctl.c b/kernel/sysctl.c index bb260ce..eda60d9 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -1667,6 +1667,13 @@ static struct ctl_table fs_table[] = { .proc_handler = proc_doulongvec_minmax, }, { + .procname = "fs-timestamp-check-on", + .data = &timestamp_check.check_on, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = proc_dointvec, + }, + { .procname = "nr_open", .data = &sysctl_nr_open, .maxlen = sizeof(unsigned int),

timespec_trunc() function is used to truncate a filesystem timestamp to the right granularity. But, the function does not clamp tv_sec part of the timestamps according to the filesystem timestamp limits.

Also, timespec_trunc() is exclusively used for filesystem timestamps. Move the api to be part of vfs.

The replacement api: timestamp_truncate() also alters the signature of the function to accommodate filesystem timestamp clamping according to flesystem limits.

Note that the clamp_t macro is used for clamping here as vfs is not yet using struct timespec64 internally. This is required for compilation purposes. Also note that clamp won't do the right thing for timestamps beyond 2038 on 32-bit machines until the vfs uses timespec64. After the vfs is transitioned to use timespec64 for timestamps, clamp_t() can be replaced by clamp().

Signed-off-by: Deepa Dinamani deepa.kernel@gmail.com --- fs/inode.c | 32 +++++++++++++++++++++++++++++++- 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/fs/inode.c b/fs/inode.c index 7967f9c..39b875b 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -2116,6 +2116,36 @@ void inode_nohighmem(struct inode *inode) EXPORT_SYMBOL(inode_nohighmem);

/** + * timestamp_truncate - Truncate timespec to a granularity + * @t: Timespec + * @inode: inode being updated + * + * Truncate a timespec to the granularity supported by the fs + * containing the inode. Always rounds down. gran must + * not be 0 nor greater than a second (NSEC_PER_SEC, or 10^9 ns). + */ +struct timespec timestamp_truncate(struct timespec t, struct inode *inode) +{ + struct super_block *sb = inode->i_sb; + unsigned int gran = sb->s_time_gran; + + t.tv_sec = clamp_t(time64_t, t.tv_sec, sb->s_time_min, sb->s_time_max); + + /* Avoid division in the common cases 1 ns and 1 s. */ + if (gran == 1) { + /* nothing */ + } else if (gran == NSEC_PER_SEC) { + t.tv_nsec = 0; + } else if (gran > 1 && gran < NSEC_PER_SEC) { + t.tv_nsec -= t.tv_nsec % gran; + } else { + WARN(1, "illegal file time granularity: %u", gran); + } + return t; +} +EXPORT_SYMBOL(timestamp_truncate); + +/** * current_time - Return FS time * @inode: inode. * @@ -2134,6 +2164,6 @@ struct timespec current_time(struct inode *inode) return now; }

- return timespec_trunc(now, inode->i_sb->s_time_gran); + return timestamp_truncate(now, inode); } EXPORT_SYMBOL(current_time);

On Fri, Feb 24, 2017 at 05:40:59PM -0800, Deepa Dinamani wrote:

Add fields to the superblock to track the min and max timestamps supported by filesystems.

Initially, when a superblock is allocated, initialize it to the max and min values the fields can hold. Individual filesystems override these to match their actual limits.

Pseudo filesystems are assumed to always support the min and max allowable values for the fields.

Note that the time ranges are saved in type time64_t rather than time_t. This is required because if we save ranges in time_t then we would not be able to save timestamp ranges for files that support timestamps beyond y2038.

Signed-off-by: Deepa Dinamani deepa.kernel@gmail.com

fs/super.c | 2 ++ include/linux/fs.h | 3 +++ include/linux/time64.h | 2 ++ 3 files changed, 7 insertions(+)

diff --git a/fs/super.c b/fs/super.c index b8b6a08..f9c2241 100644 --- a/fs/super.c +++ b/fs/super.c @@ -247,6 +247,8 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags, s->s_maxbytes = MAX_NON_LFS; s->s_op = &default_op; s->s_time_gran = 1000000000;

• s->s_time_min = TIME64_MIN;
• s->s_time_max = TIME64_MAX;

Just out of curiosity, does this enable 64-bit timestamps for everything by default? I see that ext4 later sets its own values in fill_super; what about things like XFS that really only have 32-bit seconds fields?

--D

s->cleancache_poolid = CLEANCACHE_NO_POOL; s->s_shrink.seeks = DEFAULT_SEEKS; diff --git a/include/linux/fs.h b/include/linux/fs.h index de8ed0b..ef55dfb 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1337,6 +1337,9 @@ struct super_block { /* Granularity of c/m/atime in ns. Cannot be worse than a second */ u32 s_time_gran;

• /* Time limits for c/m/atime in seconds. */
• time64_t s_time_min;
• time64_t s_time_max;

/* * The next field is for VFS *only*. No filesystems have any business diff --git a/include/linux/time64.h b/include/linux/time64.h index 980c71b..25433b18 100644 --- a/include/linux/time64.h +++ b/include/linux/time64.h @@ -38,6 +38,8 @@ struct itimerspec64 { /* Located here for timespec[64]_valid_strict */ #define TIME64_MAX ((s64)~((u64)1 << 63)) +#define TIME64_MIN (-TIME64_MAX - 1)

#define KTIME_MAX ((s64)~((u64)1 << 63)) #define KTIME_SEC_MAX (KTIME_MAX / NSEC_PER_SEC) -- 2.7.4