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file: fix close_range() for unshare+cloexec
syzbot reported a bug when putting the last reference to a tasks file descriptor table. Debugging this showed we didn't recalculate the current maximum fd number for CLOSE_RANGE_UNSHARE | CLOSE_RANGE_CLOEXEC after we unshared the file descriptors table. So max_fd could exceed the current fdtable maximum causing us to set excessive bits. As a concrete example, let's say the user requested everything from fd 4 to ~0UL to be closed and their current fdtable size is 256 with their highest open fd being 4. With CLOSE_RANGE_UNSHARE the caller will end up with a new fdtable which has room for 64 file descriptors since that is the lowest fdtable size we accept. But now max_fd will still point to 255 and needs to be adjusted. Fix this by retrieving the correct maximum fd value in __range_cloexec(). Reported-by: syzbot+283ce5a46486d6acdbaf@syzkaller.appspotmail.com Fixes:582f1fb6b7
("fs, close_range: add flag CLOSE_RANGE_CLOEXEC") Fixes:fec8a6a691
("close_range: unshare all fds for CLOSE_RANGE_UNSHARE | CLOSE_RANGE_CLOEXEC") Cc: Christoph Hellwig <hch@lst.de> Cc: Giuseppe Scrivano <gscrivan@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Cc: stable@vger.kernel.org Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
This commit is contained in:
parent
0d02ec6b31
commit
9b5b872215
21
fs/file.c
21
fs/file.c
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@ -629,17 +629,30 @@ int close_fd(unsigned fd)
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}
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EXPORT_SYMBOL(close_fd); /* for ksys_close() */
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/**
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* last_fd - return last valid index into fd table
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* @cur_fds: files struct
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*
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* Context: Either rcu read lock or files_lock must be held.
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*
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* Returns: Last valid index into fdtable.
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*/
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static inline unsigned last_fd(struct fdtable *fdt)
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{
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return fdt->max_fds - 1;
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}
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static inline void __range_cloexec(struct files_struct *cur_fds,
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unsigned int fd, unsigned int max_fd)
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{
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struct fdtable *fdt;
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if (fd > max_fd)
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return;
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/* make sure we're using the correct maximum value */
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spin_lock(&cur_fds->file_lock);
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fdt = files_fdtable(cur_fds);
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bitmap_set(fdt->close_on_exec, fd, max_fd - fd + 1);
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max_fd = min(last_fd(fdt), max_fd);
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if (fd <= max_fd)
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bitmap_set(fdt->close_on_exec, fd, max_fd - fd + 1);
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spin_unlock(&cur_fds->file_lock);
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}
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