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Vigil@nce - Linux kernel: bypassing quota on ext4

June 2010 by Vigil@nce

This bulletin was written by Vigil@nce : http://vigilance.fr/

SYNTHESIS OF THE VULNERABILITY

On an ext4 filesystem, a local attacker can use the posix_fallocate() function, in order to create a file larger than the defined limit.

Severity: 1/4

Creation date: 01/06/2010

DESCRIPTION OF THE VULNERABILITY

The RLIMIT_FSIZE limit, defined via "ulimit -f", indicates the maximal size of a file.

The posix_fallocate() system call is used to ensure there is sufficient free space on the file system to write to a file: int posix_fallocate(int fd, off_t offset, off_t len);

The ext4_fallocate() function of the fs/ext4/extents.c file defines posix_fallocate() for an ext4 filesystem. However, this function does not honor RLIMIT_FSIZE.

On an ext4 filesystem, a local attacker can therefore use the posix_fallocate() function, in order to create a file larger than the defined limit.

ACCESS TO THE COMPLETE VIGIL@NCE BULLETIN

http://vigilance.fr/vulnerability/L...




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