From dd05add7b2b6004c5fa3a1f276f56d8668f86b65 Mon Sep 17 00:00:00 2001 From: Paulo Alcantara Date: Sat, 26 Sep 2026 19:20:30 -0300 Subject: netfs: zero the tail of a short DIO/unbuffered read The buffered read collector zero-fills the tail of a short read that stops below the inode's i_size (netfs_clear_unread()), so a read that races an extending write still returns the expected number of bytes. The non-buffered collector path does no such thing: it just records how much was transferred. Add the same zero-fill for the non-buffered case, gated on NETFS_SREQ_CLEAR_TAIL: a subreq's source sets that flag when a short result from it is known to be safe to treat as a hole, as opposed to NETFS_SREQ_HIT_EOF, which means the read genuinely ran off the end of the file and should be reported short as-is. Only CLEAR_TAIL should zero-fill here; a real EOF must stay a real short read. No source currently sets CLEAR_TAIL on an unbuffered/DIO subrequest, so this is inert on its own -- a following change teaches cifs to set it in the one case that needs it. Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item") Reviewed-by: David Howells Reviewed-by: Namjae Jeon Signed-off-by: Paulo Alcantara Cc: Christian Brauner Cc: Matthew Wilcox Cc: Ronnie Sahlberg Cc: Shyam Prasad N Cc: Tom Talpey Cc: Bharath SM Cc: stable@vger.kernel.org --- Documentation/security/digsig.rst | 101 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 101 insertions(+) create mode 100644 Documentation/security/digsig.rst (limited to 'Documentation/security/digsig.rst') diff --git a/Documentation/security/digsig.rst b/Documentation/security/digsig.rst new file mode 100644 index 000000000..de035f282 --- /dev/null +++ b/Documentation/security/digsig.rst @@ -0,0 +1,101 @@ +================================== +Digital Signature Verification API +================================== + +:Author: Dmitry Kasatkin +:Date: 06.10.2011 + + +.. CONTENTS + + 1. Introduction + 2. API + 3. User-space utilities + + +Introduction +============ + +Digital signature verification API provides a method to verify digital signature. +Currently digital signatures are used by the IMA/EVM integrity protection subsystem. + +Digital signature verification is implemented using cut-down kernel port of +GnuPG multi-precision integers (MPI) library. The kernel port provides +memory allocation errors handling, has been refactored according to kernel +coding style, and checkpatch.pl reported errors and warnings have been fixed. + +Public key and signature consist of header and MPIs:: + + struct pubkey_hdr { + uint8_t version; /* key format version */ + time_t timestamp; /* key made, always 0 for now */ + uint8_t algo; + uint8_t nmpi; + char mpi[0]; + } __packed; + + struct signature_hdr { + uint8_t version; /* signature format version */ + time_t timestamp; /* signature made */ + uint8_t algo; + uint8_t hash; + uint8_t keyid[8]; + uint8_t nmpi; + char mpi[0]; + } __packed; + +keyid equals to SHA1[12-19] over the total key content. +Signature header is used as an input to generate a signature. +Such approach insures that key or signature header could not be changed. +It protects timestamp from been changed and can be used for rollback +protection. + +API +=== + +API currently includes only 1 function:: + + digsig_verify() - digital signature verification with public key + + + /** + * digsig_verify() - digital signature verification with public key + * @keyring: keyring to search key in + * @sig: digital signature + * @sigen: length of the signature + * @data: data + * @datalen: length of the data + * @return: 0 on success, -EINVAL otherwise + * + * Verifies data integrity against digital signature. + * Currently only RSA is supported. + * Normally hash of the content is used as a data for this function. + * + */ + int digsig_verify(struct key *keyring, const char *sig, int siglen, + const char *data, int datalen); + +User-space utilities +==================== + +The signing and key management utilities evm-utils provide functionality +to generate signatures, to load keys into the kernel keyring. +Keys can be in PEM or converted to the kernel format. +When the key is added to the kernel keyring, the keyid defines the name +of the key: 5D2B05FC633EE3E8 in the example below. + +Here is example output of the keyctl utility:: + + $ keyctl show + Session Keyring + -3 --alswrv 0 0 keyring: _ses + 603976250 --alswrv 0 -1 \_ keyring: _uid.0 + 817777377 --alswrv 0 0 \_ user: kmk + 891974900 --alswrv 0 0 \_ encrypted: evm-key + 170323636 --alswrv 0 0 \_ keyring: _module + 548221616 --alswrv 0 0 \_ keyring: _ima + 128198054 --alswrv 0 0 \_ keyring: _evm + + $ keyctl list 128198054 + 1 key in keyring: + 620789745: --alswrv 0 0 user: 5D2B05FC633EE3E8 -- cgit v1.3.1