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e4608715e6
The helper binary pt_chown tricked into granting access to another user's pseudo-terminal. Pre-conditions for the attack: * Attacker with local user account * Kernel with FUSE support * "user_allow_other" in /etc/fuse.conf * Victim with allocated slave in /dev/pts Using the setuid installed pt_chown and a weak check on whether a file descriptor is a tty, an attacker could fake a pty check using FUSE and trick pt_chown to grant ownership of a pty descriptor that the current user does not own. It cannot access /dev/pts/ptmx however. In most modern distributions pt_chown is not needed because devpts is enabled by default. The fix for this CVE is to disable building and using pt_chown by default. We still provide a configure option to enable hte use of pt_chown but distributions do so at their own risk.
45 lines
1.0 KiB
C
45 lines
1.0 KiB
C
#include <assert.h>
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#include <ctype.h>
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#include <dirent.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <paths.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <not-cancel.h>
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#include "pty-private.h"
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#if HAVE_PT_CHOWN
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/* Close all file descriptors except the one specified. */
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static void
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close_all_fds (void)
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{
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DIR *dir = __opendir ("/proc/self/fd");
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if (dir != NULL)
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{
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struct dirent64 *d;
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while ((d = __readdir64 (dir)) != NULL)
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if (isdigit (d->d_name[0]))
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{
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char *endp;
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long int fd = strtol (d->d_name, &endp, 10);
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if (*endp == '\0' && fd != PTY_FILENO && fd != dirfd (dir))
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close_not_cancel_no_status (fd);
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}
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__closedir (dir);
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int nullfd = open_not_cancel_2 (_PATH_DEVNULL, O_RDONLY);
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assert (nullfd == STDIN_FILENO);
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nullfd = open_not_cancel_2 (_PATH_DEVNULL, O_WRONLY);
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assert (nullfd == STDOUT_FILENO);
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__dup2 (STDOUT_FILENO, STDERR_FILENO);
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}
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}
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# define CLOSE_ALL_FDS() close_all_fds()
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#endif
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#include <sysdeps/unix/grantpt.c>
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