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kldxref: Properly handle reading strings near the end of an ELF file
If a string is at or near the end of an input file and the amount of remaining data in the file is smaller than the maximum string size, the pread(2) system call would return a short read which is treated as an error. Instead, add a new helper function for reading a string which permits short reads so long as the data read from the file contains a terminated string. Reported by: jrtc27 Reviewed by: jrtc27 Sponsored by: University of Cambridge, Google, Inc. Differential Revision: https://reviews.freebsd.org/D44419
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@ -549,7 +549,6 @@ static int
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ef_seg_read_string(elf_file_t ef, GElf_Addr address, size_t len, char *dest)
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{
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GElf_Off ofs;
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int error;
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ofs = ef_get_offset(ef, address);
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if (ofs == 0) {
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@ -559,13 +558,7 @@ ef_seg_read_string(elf_file_t ef, GElf_Addr address, size_t len, char *dest)
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return (EFAULT);
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}
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error = elf_read_raw_data(ef->ef_efile, ofs, dest, len);
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if (error != 0)
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return (error);
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if (strnlen(dest, len) == len)
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return (EFAULT);
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return (0);
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return (elf_read_raw_string(ef->ef_efile, ofs, dest, len));
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}
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int
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@ -189,6 +189,10 @@ int elf_read_raw_data(struct elf_file *efile, off_t offset, void *dst,
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int elf_read_raw_data_alloc(struct elf_file *efile, off_t offset,
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size_t len, void **out);
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/* Reads a single string at the given offset from an ELF file. */
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int elf_read_raw_string(struct elf_file *efile, off_t offset, char *dst,
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size_t len);
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/*
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* Read relocated data from an ELF file and return it in a
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* dynamically-allocated buffer. Note that no translation
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@ -248,7 +248,6 @@ static int
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ef_obj_seg_read_string(elf_file_t ef, GElf_Addr address, size_t len, char *dest)
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{
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GElf_Off ofs;
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int error;
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ofs = ef_obj_get_offset(ef, address);
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if (ofs == 0) {
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@ -258,13 +257,7 @@ ef_obj_seg_read_string(elf_file_t ef, GElf_Addr address, size_t len, char *dest)
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return (EFAULT);
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}
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error = elf_read_raw_data(ef->ef_efile, ofs, dest, len);
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if (error != 0)
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return (error);
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if (strnlen(dest, len) == len)
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return (EFAULT);
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return (0);
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return (elf_read_raw_string(ef->ef_efile, ofs, dest, len));
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}
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int
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@ -197,6 +197,24 @@ elf_read_raw_data_alloc(struct elf_file *efile, off_t offset, size_t len,
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return (0);
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}
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int
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elf_read_raw_string(struct elf_file *efile, off_t offset, char *dst, size_t len)
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{
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ssize_t nread;
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nread = pread(efile->ef_fd, dst, len, offset);
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if (nread == -1)
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return (errno);
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if (nread == 0)
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return (EIO);
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/* A short read is ok so long as the data contains a terminator. */
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if (strnlen(dst, nread) == nread)
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return (EFAULT);
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return (0);
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}
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int
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elf_read_data(struct elf_file *efile, Elf_Type type, off_t offset, size_t len,
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void **out)
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