Messages in this thread Patch in this message | | | From | Brian Norris <> | Subject | [PATCH v3] debugfs: Only clobber mode/uid/gid on remount if asked | Date | Mon, 12 Sep 2022 16:31:42 -0700 |
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Users may have explicitly configured their debugfs permissions; we shouldn't overwrite those just because a second mount appeared.
Only clobber if the options were provided at mount time.
Existing behavior:
## Pre-existing status: debugfs is 0755. # chmod 755 /sys/kernel/debug/ # stat -c '%A' /sys/kernel/debug/ drwxr-xr-x
## New mount sets kernel-default permissions: # mount -t debugfs none /mnt/foo # stat -c '%A' /mnt/foo drwx------
## Unexpected: the original mount changed permissions: # stat -c '%A' /sys/kernel/debug drwx------
New behavior:
## Pre-existing status: debugfs is 0755. # chmod 755 /sys/kernel/debug/ # stat -c '%A' /sys/kernel/debug/ drwxr-xr-x
## New mount inherits existing permissions: # mount -t debugfs none /mnt/foo # stat -c '%A' /mnt/foo drwxr-xr-x
## Expected: old mount is unchanged: # stat -c '%A' /sys/kernel/debug drwxr-xr-x
Full test cases are being submitted to LTP.
Signed-off-by: Brian Norris <briannorris@chromium.org> --- Temporary LTP branch here: https://github.com/computersforpeace/ltp/commits/debugfs
I'll put in an LTP pull request once the kernel tree actually contains my patches.
Companion patch: tracefs: Only clobber mode/uid/gid on remount if asked https://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git/commit/?h=trace-v6.0-rc4&id=47311db8e8f33011d90dee76b39c8886120cdda4
Changes in v3: * Factor out _debugfs_apply_options() to hide boolean arg * Drop unused return value
Changes in v2: * Update commit description * Include LTP patch in notes * Split from tracefs patch
fs/debugfs/inode.c | 37 ++++++++++++++++++++++++++++++------- 1 file changed, 30 insertions(+), 7 deletions(-)
diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c index 3dcf0b8b4e93..83749cd67e0d 100644 --- a/fs/debugfs/inode.c +++ b/fs/debugfs/inode.c @@ -82,6 +82,8 @@ struct debugfs_mount_opts { kuid_t uid; kgid_t gid; umode_t mode; + /* Opt_* bitfield. */ + unsigned int opts; }; enum { @@ -111,6 +113,7 @@ static int debugfs_parse_options(char *data, struct debugfs_mount_opts *opts) kgid_t gid; char *p; + opts->opts = 0; opts->mode = DEBUGFS_DEFAULT_MODE; while ((p = strsep(&data, ",")) != NULL) { @@ -145,24 +148,44 @@ static int debugfs_parse_options(char *data, struct debugfs_mount_opts *opts) * but traditionally debugfs has ignored all mount options */ } + + opts->opts |= BIT(token); } return 0; } -static int debugfs_apply_options(struct super_block *sb) +static void _debugfs_apply_options(struct super_block *sb, bool remount) { struct debugfs_fs_info *fsi = sb->s_fs_info; struct inode *inode = d_inode(sb->s_root); struct debugfs_mount_opts *opts = &fsi->mount_opts; - inode->i_mode &= ~S_IALLUGO; - inode->i_mode |= opts->mode; + /* + * On remount, only reset mode/uid/gid if they were provided as mount + * options. + */ - inode->i_uid = opts->uid; - inode->i_gid = opts->gid; + if (!remount || opts->opts & BIT(Opt_mode)) { + inode->i_mode &= ~S_IALLUGO; + inode->i_mode |= opts->mode; + } - return 0; + if (!remount || opts->opts & BIT(Opt_uid)) + inode->i_uid = opts->uid; + + if (!remount || opts->opts & BIT(Opt_gid)) + inode->i_gid = opts->gid; +} + +static void debugfs_apply_options(struct super_block *sb) +{ + _debugfs_apply_options(sb, false); +} + +static void debugfs_apply_options_remount(struct super_block *sb) +{ + _debugfs_apply_options(sb, true); } static int debugfs_remount(struct super_block *sb, int *flags, char *data) @@ -175,7 +198,7 @@ static int debugfs_remount(struct super_block *sb, int *flags, char *data) if (err) goto fail; - debugfs_apply_options(sb); + debugfs_apply_options_remount(sb); fail: return err; -- 2.37.2.789.g6183377224-goog
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