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keyctl_read(3) — Linux manual page

KEYCTL_READ(3)          Linux Key Management CallsKEYCTL_READ(3)

NAME        top

       keyctl_read - read a key

SYNOPSIS        top

#include <keyutils.h>long keyctl_read(key_serial_tkey, char *buffer, size_tbuflen);long keyctl_read_alloc(key_serial_tkey, void **_buffer);

DESCRIPTION        top

keyctl_read() reads the payload of a key if the key type supports       it.       The caller must havereadpermission on a key to be able to read       it.buffer andbuflen specify the buffer into which the payload data       will be placed.  If the buffer is too small, then the full size of       the payload will be returned, and the contents of the buffer may       be overwritten in some undefined way.keyctl_read_alloc() is similar tokeyctl_read() except that it       allocates a buffer big enough to hold the payload data and places       the data in it.  If successful, a pointer to the buffer is placed       in*_buffer.  The caller must free the buffer.keyctl_read_alloc() adds a NUL character after the data it       retrieves, though this is not counted in the size value it       returns.

READING KEYRINGS        top

       This call can be used to list the contents of a keyring.  The data       is presented to the user as an array ofkey_serial_tvalues, each       of which corresponds to a key to which the keyring holds a link.       The size of the keyring will be sizeof(key_serial_t) multiplied by       the number of keys.  The size of key_serial_t is invariant across       different word sizes, though the byte-ordering is as appropriate       for the kernel.

RETURN VALUE        top

       On successkeyctl_read() returns the amount of data placed into       the buffer.  If the buffer was too small, then the size of buffer       required will be returned, and the contents of the buffer may have       been overwritten in some undefined way.       On successkeyctl_read_alloc() returns the amount of data in the       buffer.       On error, both functions seterrno to an appropriate code and       return the value-1.

ERRORS        top

ENOKEYThe key specified is invalid.EKEYEXPIRED              The key specified has expired.EKEYREVOKED              The key specified had been revoked.EACCESThe key exists, but is notreadableby the calling process.EOPNOTSUPP              The key type does not support reading of the payload data.

LINKING        top

       This is a library function that can be found inlibkeyutils.  When       linking,-lkeyutilsshould be specified to the linker.

SEE ALSO        top

keyctl(1),add_key(2),keyctl(2),request_key(2),keyctl(3),keyrings(7),keyutils(7)

COLOPHON        top

       This page is part of thekeyutils (key management utilities)       project.  Information about the project can be found at [unknown       -- if you know, please contact man-pages@man7.org] If you have a       bug report for this manual page, send it to       keyrings@linux-nfs.org.  This page was obtained from the project's       upstream Git repository       ⟨http://git.kernel.org/pub/scm/linux/kernel/git/dhowells/keyutils.git⟩       on 2025-08-11.  (At that time, the date of the most recent commit       that was found in the repository was 2023-03-20.)  If you discover       any rendering problems in this HTML version of the page, or you       believe there is a better or more up-to-date source for the page,       or you have corrections or improvements to the information in this       COLOPHON (which isnot part of the original manual page), send a       mail to man-pages@man7.orgLinux                          21 Feb 2014KEYCTL_READ(3)

Pages that refer to this page:KEYCTL_READ(2const), request_key(2), keyctl(3)

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