Commit 156cacb1d0d36b0d0582d9e798e58e0044f516b3
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fea7a08acb
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do_add_mount()/umount -l races
normally we deal with lock_mount()/umount races by checking that mountpoint to be is still in our namespace after lock_mount() has been done. However, do_add_mount() skips that check when called with MNT_SHRINKABLE in flags (i.e. from finish_automount()). The reason is that ->mnt_ns may be a temporary namespace created exactly to contain automounts a-la NFS4 referral handling. It's not the namespace of the caller, though, so check_mnt() would fail here. We still need to check that ->mnt_ns is non-NULL in that case, though. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Showing 1 changed file with 8 additions and 2 deletions Side-by-side Diff
fs/namespace.c
... | ... | @@ -1886,8 +1886,14 @@ |
1886 | 1886 | return err; |
1887 | 1887 | |
1888 | 1888 | err = -EINVAL; |
1889 | - if (!(mnt_flags & MNT_SHRINKABLE) && !check_mnt(real_mount(path->mnt))) | |
1890 | - goto unlock; | |
1889 | + if (unlikely(!check_mnt(real_mount(path->mnt)))) { | |
1890 | + /* that's acceptable only for automounts done in private ns */ | |
1891 | + if (!(mnt_flags & MNT_SHRINKABLE)) | |
1892 | + goto unlock; | |
1893 | + /* ... and for those we'd better have mountpoint still alive */ | |
1894 | + if (!real_mount(path->mnt)->mnt_ns) | |
1895 | + goto unlock; | |
1896 | + } | |
1891 | 1897 | |
1892 | 1898 | /* Refuse the same filesystem on the same mount point */ |
1893 | 1899 | err = -EBUSY; |