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Commit 2f46a2bc authored by Eric Biggers's avatar Eric Biggers Committed by Theodore Ts'o
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fscrypt: document symlink length restriction 



Document that encryption reduces the maximum length of a symlink target
slightly.

Signed-off-by: default avatarEric Biggers <ebiggers@google.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent b9db0b4a

Documentation/filesystems/fscrypt.rst

+8 −2
Original line number Diff line number Diff line
@@ -448,8 +448,14 @@ astute users may notice some differences in behavior: 


- The st_size of an encrypted symlink will not necessarily give the

  length of the symlink target as required by POSIX.  It will actually

  give the length of the ciphertext, which may be slightly longer than

  the plaintext due to the NUL-padding.

  give the length of the ciphertext, which will be slightly longer

  than the plaintext due to NUL-padding and an extra 2-byte overhead.



- The maximum length of an encrypted symlink is 2 bytes shorter than

  the maximum length of an unencrypted symlink.  For example, on an

  EXT4 filesystem with a 4K block size, unencrypted symlinks can be up

  to 4095 bytes long, while encrypted symlinks can only be up to 4093

  bytes long (both lengths excluding the terminating null).



Note that mmap *is* supported.  This is possible because the pagecache

for an encrypted file contains the plaintext, not the ciphertext.