| Message ID | 20181017041744.1232-2-po-hsu.lin@canonical.com |
|---|---|
| State | New |
| Headers | show |
| Series | getxattr: use correct xattr length | expand |
On 17.10.18 06:17, Po-Hsu Lin wrote: > From: Christian Brauner <christian@brauner.io> > > BugLink: https://bugs.launchpad.net/bugs/1798013 > > When running in a container with a user namespace, if you call getxattr > with name = "system.posix_acl_access" and size % 8 != 4, then getxattr > silently skips the user namespace fixup that it normally does resulting in > un-fixed-up data being returned. > This is caused by posix_acl_fix_xattr_to_user() being passed the total > buffer size and not the actual size of the xattr as returned by > vfs_getxattr(). > This commit passes the actual length of the xattr as returned by > vfs_getxattr() down. > > A reproducer for the issue is: > > touch acl_posix > > setfacl -m user:0:rwx acl_posix > > and the compile: > > #define _GNU_SOURCE > #include <errno.h> > #include <stdio.h> > #include <stdlib.h> > #include <string.h> > #include <sys/types.h> > #include <unistd.h> > #include <attr/xattr.h> > > /* Run in user namespace with nsuid 0 mapped to uid != 0 on the host. */ > int main(int argc, void **argv) > { > ssize_t ret1, ret2; > char buf1[128], buf2[132]; > int fret = EXIT_SUCCESS; > char *file; > > if (argc < 2) { > fprintf(stderr, > "Please specify a file with " > "\"system.posix_acl_access\" permissions set\n"); > _exit(EXIT_FAILURE); > } > file = argv[1]; > > ret1 = getxattr(file, "system.posix_acl_access", > buf1, sizeof(buf1)); > if (ret1 < 0) { > fprintf(stderr, "%s - Failed to retrieve " > "\"system.posix_acl_access\" " > "from \"%s\"\n", strerror(errno), file); > _exit(EXIT_FAILURE); > } > > ret2 = getxattr(file, "system.posix_acl_access", > buf2, sizeof(buf2)); > if (ret2 < 0) { > fprintf(stderr, "%s - Failed to retrieve " > "\"system.posix_acl_access\" " > "from \"%s\"\n", strerror(errno), file); > _exit(EXIT_FAILURE); > } > > if (ret1 != ret2) { > fprintf(stderr, "The value of \"system.posix_acl_" > "access\" for file \"%s\" changed " > "between two successive calls\n", file); > _exit(EXIT_FAILURE); > } > > for (ssize_t i = 0; i < ret2; i++) { > if (buf1[i] == buf2[i]) > continue; > > fprintf(stderr, > "Unexpected different in byte %zd: " > "%02x != %02x\n", i, buf1[i], buf2[i]); > fret = EXIT_FAILURE; > } > > if (fret == EXIT_SUCCESS) > fprintf(stderr, "Test passed\n"); > else > fprintf(stderr, "Test failed\n"); > > _exit(fret); > } > and run: > > ./tester acl_posix > > On a non-fixed up kernel this should return something like: > > root@c1:/# ./t > Unexpected different in byte 16: ffffffa0 != 00 > Unexpected different in byte 17: ffffff86 != 00 > Unexpected different in byte 18: 01 != 00 > > and on a fixed kernel: > > root@c1:~# ./t > Test passed > > Cc: stable@vger.kernel.org > Fixes: 2f6f0654ab61 ("userns: Convert vfs posix_acl support to use kuids and kgids") > Link: https://bugzilla.kernel.org/show_bug.cgi?id=199945 > Reported-by: Colin Watson <cjwatson@ubuntu.com> > Signed-off-by: Christian Brauner <christian@brauner.io> > Acked-by: Serge Hallyn <serge@hallyn.com> > Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> > (cherry picked from commit 82c9a927bc5df6e06b72d206d24a9d10cced4eb5) > Signed-off-by: Po-Hsu Lin <po-hsu.lin@canonical.com> Acked-by: Stefan Bader <stefan.bader@canonical.com> > --- > fs/xattr.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/xattr.c b/fs/xattr.c > index 3377dff..afc74ba 100644 > --- a/fs/xattr.c > +++ b/fs/xattr.c > @@ -466,7 +466,7 @@ getxattr(struct dentry *d, const char __user *name, void __user *value, > if (error > 0) { > if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) || > (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0)) > - posix_acl_fix_xattr_to_user(kvalue, size); > + posix_acl_fix_xattr_to_user(kvalue, error); > if (size && copy_to_user(value, kvalue, error)) > error = -EFAULT; > } else if (error == -ERANGE && size >= XATTR_SIZE_MAX) { >
On 10/17/18 06:17, Po-Hsu Lin wrote: > From: Christian Brauner <christian@brauner.io> > > BugLink: https://bugs.launchpad.net/bugs/1798013 > > When running in a container with a user namespace, if you call getxattr > with name = "system.posix_acl_access" and size % 8 != 4, then getxattr > silently skips the user namespace fixup that it normally does resulting in > un-fixed-up data being returned. > This is caused by posix_acl_fix_xattr_to_user() being passed the total > buffer size and not the actual size of the xattr as returned by > vfs_getxattr(). > This commit passes the actual length of the xattr as returned by > vfs_getxattr() down. > > A reproducer for the issue is: > > touch acl_posix > > setfacl -m user:0:rwx acl_posix > > and the compile: > > #define _GNU_SOURCE > #include <errno.h> > #include <stdio.h> > #include <stdlib.h> > #include <string.h> > #include <sys/types.h> > #include <unistd.h> > #include <attr/xattr.h> > > /* Run in user namespace with nsuid 0 mapped to uid != 0 on the host. */ > int main(int argc, void **argv) > { > ssize_t ret1, ret2; > char buf1[128], buf2[132]; > int fret = EXIT_SUCCESS; > char *file; > > if (argc < 2) { > fprintf(stderr, > "Please specify a file with " > "\"system.posix_acl_access\" permissions set\n"); > _exit(EXIT_FAILURE); > } > file = argv[1]; > > ret1 = getxattr(file, "system.posix_acl_access", > buf1, sizeof(buf1)); > if (ret1 < 0) { > fprintf(stderr, "%s - Failed to retrieve " > "\"system.posix_acl_access\" " > "from \"%s\"\n", strerror(errno), file); > _exit(EXIT_FAILURE); > } > > ret2 = getxattr(file, "system.posix_acl_access", > buf2, sizeof(buf2)); > if (ret2 < 0) { > fprintf(stderr, "%s - Failed to retrieve " > "\"system.posix_acl_access\" " > "from \"%s\"\n", strerror(errno), file); > _exit(EXIT_FAILURE); > } > > if (ret1 != ret2) { > fprintf(stderr, "The value of \"system.posix_acl_" > "access\" for file \"%s\" changed " > "between two successive calls\n", file); > _exit(EXIT_FAILURE); > } > > for (ssize_t i = 0; i < ret2; i++) { > if (buf1[i] == buf2[i]) > continue; > > fprintf(stderr, > "Unexpected different in byte %zd: " > "%02x != %02x\n", i, buf1[i], buf2[i]); > fret = EXIT_FAILURE; > } > > if (fret == EXIT_SUCCESS) > fprintf(stderr, "Test passed\n"); > else > fprintf(stderr, "Test failed\n"); > > _exit(fret); > } > and run: > > ./tester acl_posix > > On a non-fixed up kernel this should return something like: > > root@c1:/# ./t > Unexpected different in byte 16: ffffffa0 != 00 > Unexpected different in byte 17: ffffff86 != 00 > Unexpected different in byte 18: 01 != 00 > > and on a fixed kernel: > > root@c1:~# ./t > Test passed > > Cc: stable@vger.kernel.org > Fixes: 2f6f0654ab61 ("userns: Convert vfs posix_acl support to use kuids and kgids") > Link: https://bugzilla.kernel.org/show_bug.cgi?id=199945 > Reported-by: Colin Watson <cjwatson@ubuntu.com> > Signed-off-by: Christian Brauner <christian@brauner.io> > Acked-by: Serge Hallyn <serge@hallyn.com> > Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> > (cherry picked from commit 82c9a927bc5df6e06b72d206d24a9d10cced4eb5) > Signed-off-by: Po-Hsu Lin <po-hsu.lin@canonical.com> Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com> > --- > fs/xattr.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/xattr.c b/fs/xattr.c > index 3377dff..afc74ba 100644 > --- a/fs/xattr.c > +++ b/fs/xattr.c > @@ -466,7 +466,7 @@ getxattr(struct dentry *d, const char __user *name, void __user *value, > if (error > 0) { > if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) || > (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0)) > - posix_acl_fix_xattr_to_user(kvalue, size); > + posix_acl_fix_xattr_to_user(kvalue, error); > if (size && copy_to_user(value, kvalue, error)) > error = -EFAULT; > } else if (error == -ERANGE && size >= XATTR_SIZE_MAX) { >
On 17/10/2018 05:17, Po-Hsu Lin wrote: > From: Christian Brauner <christian@brauner.io> > > BugLink: https://bugs.launchpad.net/bugs/1798013 > > When running in a container with a user namespace, if you call getxattr > with name = "system.posix_acl_access" and size % 8 != 4, then getxattr > silently skips the user namespace fixup that it normally does resulting in > un-fixed-up data being returned. > This is caused by posix_acl_fix_xattr_to_user() being passed the total > buffer size and not the actual size of the xattr as returned by > vfs_getxattr(). > This commit passes the actual length of the xattr as returned by > vfs_getxattr() down. > > A reproducer for the issue is: > > touch acl_posix > > setfacl -m user:0:rwx acl_posix > > and the compile: > > #define _GNU_SOURCE > #include <errno.h> > #include <stdio.h> > #include <stdlib.h> > #include <string.h> > #include <sys/types.h> > #include <unistd.h> > #include <attr/xattr.h> > > /* Run in user namespace with nsuid 0 mapped to uid != 0 on the host. */ > int main(int argc, void **argv) > { > ssize_t ret1, ret2; > char buf1[128], buf2[132]; > int fret = EXIT_SUCCESS; > char *file; > > if (argc < 2) { > fprintf(stderr, > "Please specify a file with " > "\"system.posix_acl_access\" permissions set\n"); > _exit(EXIT_FAILURE); > } > file = argv[1]; > > ret1 = getxattr(file, "system.posix_acl_access", > buf1, sizeof(buf1)); > if (ret1 < 0) { > fprintf(stderr, "%s - Failed to retrieve " > "\"system.posix_acl_access\" " > "from \"%s\"\n", strerror(errno), file); > _exit(EXIT_FAILURE); > } > > ret2 = getxattr(file, "system.posix_acl_access", > buf2, sizeof(buf2)); > if (ret2 < 0) { > fprintf(stderr, "%s - Failed to retrieve " > "\"system.posix_acl_access\" " > "from \"%s\"\n", strerror(errno), file); > _exit(EXIT_FAILURE); > } > > if (ret1 != ret2) { > fprintf(stderr, "The value of \"system.posix_acl_" > "access\" for file \"%s\" changed " > "between two successive calls\n", file); > _exit(EXIT_FAILURE); > } > > for (ssize_t i = 0; i < ret2; i++) { > if (buf1[i] == buf2[i]) > continue; > > fprintf(stderr, > "Unexpected different in byte %zd: " > "%02x != %02x\n", i, buf1[i], buf2[i]); > fret = EXIT_FAILURE; > } > > if (fret == EXIT_SUCCESS) > fprintf(stderr, "Test passed\n"); > else > fprintf(stderr, "Test failed\n"); > > _exit(fret); > } > and run: > > ./tester acl_posix > > On a non-fixed up kernel this should return something like: > > root@c1:/# ./t > Unexpected different in byte 16: ffffffa0 != 00 > Unexpected different in byte 17: ffffff86 != 00 > Unexpected different in byte 18: 01 != 00 > > and on a fixed kernel: > > root@c1:~# ./t > Test passed > > Cc: stable@vger.kernel.org > Fixes: 2f6f0654ab61 ("userns: Convert vfs posix_acl support to use kuids and kgids") > Link: https://bugzilla.kernel.org/show_bug.cgi?id=199945 > Reported-by: Colin Watson <cjwatson@ubuntu.com> > Signed-off-by: Christian Brauner <christian@brauner.io> > Acked-by: Serge Hallyn <serge@hallyn.com> > Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> > (cherry picked from commit 82c9a927bc5df6e06b72d206d24a9d10cced4eb5) > Signed-off-by: Po-Hsu Lin <po-hsu.lin@canonical.com> > --- > fs/xattr.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/xattr.c b/fs/xattr.c > index 3377dff..afc74ba 100644 > --- a/fs/xattr.c > +++ b/fs/xattr.c > @@ -466,7 +466,7 @@ getxattr(struct dentry *d, const char __user *name, void __user *value, > if (error > 0) { > if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) || > (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0)) > - posix_acl_fix_xattr_to_user(kvalue, size); > + posix_acl_fix_xattr_to_user(kvalue, error); > if (size && copy_to_user(value, kvalue, error)) > error = -EFAULT; > } else if (error == -ERANGE && size >= XATTR_SIZE_MAX) { > Clean cherry pick. Acked-by: Colin Ian King <colin.king@canonical.com>
diff --git a/fs/xattr.c b/fs/xattr.c index 3377dff..afc74ba 100644 --- a/fs/xattr.c +++ b/fs/xattr.c @@ -466,7 +466,7 @@ getxattr(struct dentry *d, const char __user *name, void __user *value, if (error > 0) { if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) || (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0)) - posix_acl_fix_xattr_to_user(kvalue, size); + posix_acl_fix_xattr_to_user(kvalue, error); if (size && copy_to_user(value, kvalue, error)) error = -EFAULT; } else if (error == -ERANGE && size >= XATTR_SIZE_MAX) {