Resolve "`cat` and other system commands use (new)fstatat with AT_EMPTY_PATH flag"

Ramon Nourequested to merge
rnou/228-cat-and-other-system-commands-use-new-fstatat-with-at_empty_path-flag into master

Before this MR: The flag is ignored in relativize_fd_path, but the man page shows that dirfd can be a file if the EMPTY_PATH is on. It seems that newer (kernel/coreutils/etc) uses that instead of doing a normal stat to the file.

Therefore, we need to handle empty path during relativize paths so that the file descriptor is used instead.

Closes #228 (closed)

Edited by Marc Vef

Merge request reports

include/client/preload_context.hpp

+1 −1
Changes for include/client/preload_context.hpp: 1 added line, 1 removed line.
Original line number Diff line number Diff line
@@ -170,7 +170,7 @@ public: 


    RelativizeStatus

    relativize_fd_path(int dirfd, const char* raw_path,

                       std::string& relative_path,

                       std::string& relative_path, int flags = 0,

                       bool resolve_last_link = true) const;



    bool

src/client/hooks.cpp

+1 −1
Changes for src/client/hooks.cpp: 1 added line, 1 removed line.
Original line number Diff line number Diff line
@@ -203,7 +203,7 @@ hook_fstatat(int dirfd, const char* cpath, struct stat* buf, int flags) { 
        __func__, cpath, dirfd, fmt::ptr(buf), flags);



    std::string resolved;

    auto rstatus = CTX->relativize_fd_path(dirfd, cpath, resolved);

    auto rstatus = CTX->relativize_fd_path(dirfd, cpath, resolved, flags);

    switch(rstatus) {

        case gkfs::preload::RelativizeStatus::fd_unknown:

            return syscall_no_intercept_wrapper(SYS_newfstatat, dirfd, cpath,

src/client/preload_context.cpp

+8 −1
Changes for src/client/preload_context.cpp: 8 added lines, 1 removed line.
Original line number Diff line number Diff line
@@ -185,7 +185,7 @@ PreloadContext::auto_sm(bool auto_sm) { 


RelativizeStatus

PreloadContext::relativize_fd_path(int dirfd, const char* raw_path,

                                   std::string& relative_path,

                                   std::string& relative_path, int flags,

                                   bool resolve_last_link) const {



    // Relativize path should be called only after the library constructor has
@@ -207,6 +207,13 @@ PreloadContext::relativize_fd_path(int dirfd, const char* raw_path, 
        } else {

            if(!ofm_->exist(dirfd)) {

                return RelativizeStatus::fd_unknown;

            } else {

                // check if we have the AT_EMPTY_PATH flag

                // for fstatat.

                if(flags & AT_EMPTY_PATH) {

                    relative_path = ofm_->get(dirfd)->path();

                    return RelativizeStatus::internal;

                }

            }

            // path is relative to fd

            auto dir = ofm_->get_dir(dirfd);

CHANGELOG.md

+2 −0
Changes for CHANGELOG.md: 2 added lines, 0 removed lines.
Original line number Diff line number Diff line
@@ -21,6 +21,8 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html). 
### Fixed

- Using `unlink` now fails if it is a directory unless the `AT_REMOVEDIR` flag is used (POSIX compliance) ([!139](https://storage.bsc.es/gitlab/hpc/gekkofs/-/merge_requests/139)).

- fchdir generate a SIGSEV in debug mode (due to log) ([!141](https://storage.bsc.es/gitlab/hpc/gekkofs/-/merge_requests/141))

- Fix fstatat to be able to understand `AT_EMPTY_PATH` flag used in coreutils (`cat` ...) ([!149](https://storage.bsc.es/gitlab/hpc/gekkofs/-/merge_requests/149)).



## [0.9.1] - 2022-04-29



### New