diff options
Diffstat (limited to 'lib/careadlinkat.c')
| -rw-r--r-- | lib/careadlinkat.c | 176 |
1 files changed, 100 insertions, 76 deletions
diff --git a/lib/careadlinkat.c b/lib/careadlinkat.c index e2af54f0984..6ddc35f798b 100644 --- a/lib/careadlinkat.c +++ b/lib/careadlinkat.c @@ -1,19 +1,19 @@ /* Read symbolic links into a buffer without size limitation, relative to fd. - Copyright (C) 2001, 2003-2004, 2007, 2009-2017 Free Software Foundation, + Copyright (C) 2001, 2003-2004, 2007, 2009-2022 Free Software Foundation, Inc. - This program is free software: you can redistribute it and/or modify - it under the terms of the GNU General Public License as published by - the Free Software Foundation; either version 3 of the License, or - (at your option) any later version. + This file is free software: you can redistribute it and/or modify + it under the terms of the GNU Lesser General Public License as + published by the Free Software Foundation; either version 2.1 of the + License, or (at your option) any later version. - This program is distributed in the hope that it will be useful, + This file is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - GNU General Public License for more details. + GNU Lesser General Public License for more details. - You should have received a copy of the GNU General Public License + You should have received a copy of the GNU Lesser General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. */ /* Written by Paul Eggert, Bruno Haible, and Jim Meyering. */ @@ -22,6 +22,9 @@ #include "careadlinkat.h" +#include "idx.h" +#include "minmax.h" + #include <errno.h> #include <limits.h> #include <string.h> @@ -38,78 +41,62 @@ #include "allocator.h" -/* Assuming the current directory is FD, get the symbolic link value - of FILENAME as a null-terminated string and put it into a buffer. - If FD is AT_FDCWD, FILENAME is interpreted relative to the current - working directory, as in openat. - - If the link is small enough to fit into BUFFER put it there. - BUFFER's size is BUFFER_SIZE, and BUFFER can be null - if BUFFER_SIZE is zero. - - If the link is not small, put it into a dynamically allocated - buffer managed by ALLOC. It is the caller's responsibility to free - the returned value if it is nonnull and is not BUFFER. A null - ALLOC stands for the standard allocator. - - The PREADLINKAT function specifies how to read links. It operates - like POSIX readlinkat() - <http://pubs.opengroup.org/onlinepubs/9699919799/functions/readlink.html> - but can assume that its first argument is the same as FD. - - If successful, return the buffer address; otherwise return NULL and - set errno. */ - -char * -careadlinkat (int fd, char const *filename, +enum { STACK_BUF_SIZE = 1024 }; + +/* Act like careadlinkat (see below), with an additional argument + STACK_BUF that can be used as temporary storage. + + If GCC_LINT is defined, do not inline this function with GCC 10.1 + and later, to avoid creating a pointer to the stack that GCC + -Wreturn-local-addr incorrectly complains about. See: + https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93644 + Although the noinline attribute can hurt performance a bit, no better way + to pacify GCC is known; even an explicit #pragma does not pacify GCC. + When the GCC bug is fixed this workaround should be limited to the + broken GCC versions. */ +#if _GL_GNUC_PREREQ (10, 1) +# if defined GCC_LINT || defined lint +__attribute__ ((__noinline__)) +# elif __OPTIMIZE__ && !__NO_INLINE__ +# define GCC_BOGUS_WRETURN_LOCAL_ADDR +# endif +#endif +static char * +readlink_stk (int fd, char const *filename, char *buffer, size_t buffer_size, struct allocator const *alloc, - ssize_t (*preadlinkat) (int, char const *, char *, size_t)) + ssize_t (*preadlinkat) (int, char const *, char *, size_t), + char stack_buf[STACK_BUF_SIZE]) { - char *buf; - size_t buf_size; - size_t buf_size_max = - SSIZE_MAX < SIZE_MAX ? (size_t) SSIZE_MAX + 1 : SIZE_MAX; - char stack_buf[1024]; - if (! alloc) alloc = &stdlib_allocator; - if (! buffer_size) + if (!buffer) { - /* Allocate the initial buffer on the stack. This way, in the - common case of a symlink of small size, we get away with a - single small malloc() instead of a big malloc() followed by a - shrinking realloc(). */ buffer = stack_buf; - buffer_size = sizeof stack_buf; + buffer_size = STACK_BUF_SIZE; } - buf = buffer; - buf_size = buffer_size; + char *buf = buffer; + idx_t buf_size_max = MIN (IDX_MAX, MIN (SSIZE_MAX, SIZE_MAX)); + idx_t buf_size = MIN (buffer_size, buf_size_max); - do + while (buf) { /* Attempt to read the link into the current buffer. */ - ssize_t link_length = preadlinkat (fd, filename, buf, buf_size); - size_t link_size; + idx_t link_length = preadlinkat (fd, filename, buf, buf_size); if (link_length < 0) { - /* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1 - with errno == ERANGE if the buffer is too small. */ - int readlinkat_errno = errno; - if (readlinkat_errno != ERANGE) + if (buf != buffer) { - if (buf != buffer) - { - alloc->free (buf); - errno = readlinkat_errno; - } - return NULL; + int readlinkat_errno = errno; + alloc->free (buf); + errno = readlinkat_errno; } + return NULL; } - link_size = link_length; + idx_t link_size = link_length; if (link_size < buf_size) { @@ -117,19 +104,19 @@ careadlinkat (int fd, char const *filename, if (buf == stack_buf) { - char *b = (char *) alloc->allocate (link_size); + char *b = alloc->allocate (link_size); buf_size = link_size; if (! b) break; - memcpy (b, buf, link_size); - buf = b; + return memcpy (b, buf, link_size); } - else if (link_size < buf_size && buf != buffer && alloc->reallocate) + + if (link_size < buf_size && buf != buffer && alloc->reallocate) { /* Shrink BUF before returning it. */ - char *b = (char *) alloc->reallocate (buf, link_size); + char *b = alloc->reallocate (buf, link_size); if (b) - buf = b; + return b; } return buf; @@ -138,23 +125,60 @@ careadlinkat (int fd, char const *filename, if (buf != buffer) alloc->free (buf); - if (buf_size <= buf_size_max / 2) - buf_size *= 2; - else if (buf_size < buf_size_max) - buf_size = buf_size_max; - else if (buf_size_max < SIZE_MAX) + if (buf_size_max / 2 <= buf_size) { errno = ENAMETOOLONG; return NULL; } - else - break; - buf = (char *) alloc->allocate (buf_size); + + buf_size = 2 * buf_size + 1; + buf = alloc->allocate (buf_size); } - while (buf); if (alloc->die) alloc->die (buf_size); errno = ENOMEM; return NULL; } + + +/* Assuming the current directory is FD, get the symbolic link value + of FILENAME as a null-terminated string and put it into a buffer. + If FD is AT_FDCWD, FILENAME is interpreted relative to the current + working directory, as in openat. + + If the link is small enough to fit into BUFFER put it there. + BUFFER's size is BUFFER_SIZE, and BUFFER can be null + if BUFFER_SIZE is zero. + + If the link is not small, put it into a dynamically allocated + buffer managed by ALLOC. It is the caller's responsibility to free + the returned value if it is nonnull and is not BUFFER. A null + ALLOC stands for the standard allocator. + + The PREADLINKAT function specifies how to read links. It operates + like POSIX readlinkat() + <https://pubs.opengroup.org/onlinepubs/9699919799/functions/readlink.html> + but can assume that its first argument is the same as FD. + + If successful, return the buffer address; otherwise return NULL and + set errno. */ + +char * +careadlinkat (int fd, char const *filename, + char *buffer, size_t buffer_size, + struct allocator const *alloc, + ssize_t (*preadlinkat) (int, char const *, char *, size_t)) +{ + /* Allocate the initial buffer on the stack. This way, in the + common case of a symlink of small size, we get away with a + single small malloc instead of a big malloc followed by a + shrinking realloc. */ + #ifdef GCC_BOGUS_WRETURN_LOCAL_ADDR + #warning "GCC might issue a bogus -Wreturn-local-addr warning here." + #warning "See <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93644>." + #endif + char stack_buf[STACK_BUF_SIZE]; + return readlink_stk (fd, filename, buffer, buffer_size, alloc, + preadlinkat, stack_buf); +} |